Body Stuff Powerlifting Adaptação neural

1: Clin Physiol Funct Imaging. 2007 Mar;27(2):91-100.

Comparative effects of resistance training on peak isometric torque, muscle hypertrophy, voluntary activation and surface EMG between young and elderly women.

Cannon J, Kay D, Tarpenning KM, Marino FE.

Exercise and Sports Science Laboratories, School of Human Movement Studies, Charles Sturt University, Bathurst, NSW, Australia. jcannon@csu.edu.au

We compared the effect of a 10-week resistance training program on peak isometric torque, muscle hypertrophy, voluntary activation and electromyogram signal amplitude (EMG) of the knee extensors between young and elderly women. Nine young women (YW; range 20-30 years) and eight elderly women (EW; 64-78 years) performed three sets of ten repetitions at 75% 1 repetition maximum for the bilateral leg extension and bilateral leg curl 3 days per week for 10 weeks. Peak isometric torque, EMG and voluntary activation were assessed before, during, and after the training period, while knee extensor lean muscle cross-sectional area (LCSA) and lean muscle volume (LMV) were assessed before and after the training period only. Similar increases in peak isometric torque (16% and 18%), LCSA (13% and 12%), LMV (10% and 9%) and EMG (19% and 21%) were observed between YW and EW, respectively, at the completion of training (P<0.05), while the increase in voluntary activation in YW (1.9%) and EW (2.1%) was not significant (P>0.05). These findings provide evidence to indicate that participation in regular resistance exercise can have significant neuromuscular benefits in women independent of age. The lack of change in voluntary activation following resistance training in both age groups despite the increase in EMG may be related to differences between measurements in their ability to detect resistance training-induced changes in motor unit activity. However, it is possible that neural adaptation did not occur and that the increase in EMG was due to peripheral adaptations.

Publication Types:

PMID: 17309529 [PubMed - indexed for MEDLINE]

2: Eur J Appl Physiol. 2006 Jul;97(4):486-93. Epub 2006 Jun 9.

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Excitability of the soleus reflex arc during intensive stretch-shortening cycle exercise in two power-trained athlete groups.

Avela J, Finni J, Komi PV.

Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, 40100 Jyvaskyla, Finland. janne.avela@sport.jyu.fi

In several explosive types of sport events the leg extensor muscles are subjected to very high impact loads. Thus, extreme requirements exist for the neuromuscular system to develop sufficient muscle stiffness in the lower extremities in order to tolerate these high impact loads. Therefore, it would be challenging to measure reflex modulation during high impact activities, and with different athlete populations. In the present experiment, H-reflex and short latency reflex (M1) sensitivity was measured during drop jump exercises among high jumpers and sprinters. The changes in both reflex peak-to-peak amplitudes showed a significant (P < 0.05) reduction towards the end of the exercise for the sprinters. In addition, the same subject group showed a remarkable increase in serum creatine kinase (CK) activity 2 h after the jumps. Similar changes could not be observed for the high jumpers. These results clearly indicate different neural adaptation strategies for the two athlete groups. Reduction in H-reflex sensitivity and an increase in CK-activity in sprinters were taken as evidence for presynaptic inhibition, probably induced by substances related to muscle damage. Since high jump training includes more high impact loading, it was assumed that it could lead to some structural adaptation and, thus, prevents exercise induced reflex modification to a certain extent.

Publication Types:

Comparative Study

PMID: 16763835 [PubMed - indexed for MEDLINE]

3: Eur J Appl Physiol. 2006 Apr;96(6):722-8. Epub 2006 Feb 28.

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Chronic neural adaptation induced by long-term resistance training in humans.

del Olmo MF, Reimunde P, Viana O, Acero RM, Cudeiro J.

Department of Medicine-INEF-Galicia, Laboratory of Neuroscience and Motor Control (NEUROcom), Universidad de A Coruña, 15006 A Coruña, Spain.

While it is known that resistance training causes changes in the central nervous system (CNS) in the initial stages of training, there have been few studies of cumulative or sustained neural adaptation to resistance training beyond the initial periods. To further investigate this we compared the electromyographic (EMG) response to transcranial magnetic stimulation (TMS) during voluntary contractions of ten subjects who have been training for more than 2 years, resistance-training (RT) group, and ten subjects that have never participated in resistance training (NT). The active motor threshold for biceps brachii was obtained during voluntary elbow flexion at 10% of maximal voluntary contraction (MVC). TMS was also delivered at 100% of the maximal stimulator output while the participants exerted forces ranging from 10 to 90% of MVC. Evoked force, motor-evoked potential (MEP) amplitude and latency from biceps brachii was recorded for each condition to explore changes in corticospinal excitability. The evoked force was significantly lower in the RT group in comparison with the NT group between 30 and 70% of MVC intensity (P<0.05). At 90% of MVC, nine subjects from the RT group showed an absence in the evoked force while this occurred in only five subjects from the NT group. The MEP amplitude and latency changed significantly (P<0.001) with increasing levels of contraction, without significant difference between groups. These results indicate that changes in the CNS are sustained in the log-term practices of resistance training and permit a higher voluntary activation at several intensities of the MVC.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 16506058 [PubMed - indexed for MEDLINE]

4: Eur J Appl Physiol. 2005 Aug;94(5-6):593-601. Epub 2005 May 26.

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Changes in agonist EMG activation level during MVC cannot explain early strength improvement.

Holtermann A, Roeleveld K, Vereijken B, Ettema G.

Human Movement Sciences Program, Faculty of Social Sciences and Technology Management, Norwegian University of Science and Technology (NTNU), Dragvoll Idrettssenter, 7491 Trondheim, Norway.

A substantial gain in strength is often observed in the early phase of resistance training. The aim of this study was to address whether improved strength in the early phase of resistance training, can be attributed to increased activation, or to intra-muscular changes of the agonist muscle during maximal isometric torque production. Fourteen male subjects trained maximal isometric dorsiflexion during 5 days. Each subject performed 9 sessions with 25 maximal voluntary contractions in a device that registered the dorsiflexion torque. Surface electromyography (SEMG) of the tibialis anterior (TA) was recorded with a 130-channel grid electrode. SEMG of the extensor digitorum longus, gastrocnemius and soleus muscles were recorded with bipolar electrodes. The main finding was that all subjects gained in strength while the SEMG activation level of the primer agonist, TA, decreased with no apparent intra-muscular spatial changes following 5 days of resistance training. The other muscles that influence dorsiflexion torque did not modify their activation level with training. These findings reject an increase in agonist activation level as the main source for early strength gain, and illustrate the need for further research to reveal the specific sites of neural adaptation and other physiological mechanisms that might contribute to increased strength during the early phase of resistance training.

Publication Types:

Clinical Trial

PMID: 15918059 [PubMed - indexed for MEDLINE]

5: J Gerontol A Biol Sci Med Sci. 2003 Oct;58(10):B889-94.

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Differential effectiveness of low-intensity exercise in young and old rats.

Brown M, Taylor J, Gabriel R.

Program in Physical Therapy, Washington University School of Medicine, St Louis, Missouri 65211, USA. brownmb@health.missouri.edu

Low-intensity exercise increases strength and function in old adults, but it is unclear if change occurs secondary to "neural adaptation" or to intrinsic muscle adaptation. Whether function and strength change concomitantly is also unclear. We examined effects of a modest intensity, 10-session exercise program on muscle mass, contractile force, and function (gait) in 6-month-old and 30-month-old rats. Animals underwent 45 minutes of activity (e.g., ramp walking, balancing) 5 days/week. In old animals, a significant increase in muscle mass and peak contractile force occurred with exercise in soleus, plantaris, extensor digitorum longus, and peroneus longus compared with controls, but did not restore values to those for young controls. The increase in muscle force in old rats was accompanied by a significant lengthening of stride (90 +/- 9 to 103 +/- 15 mm), which was still 23% less than stride values for young rats. Changes in muscle function and gait with exercise were not apparent in young rats. Results suggest that (a). rapid and significant changes in muscle mass and strength in an aged organism can occur with a modest activity program, (b). the threshold for muscle adaptation may differ in young versus old rats, and (c). changes in strength and function in old rats may occur concomitantly.

Publication Types:

Research Support, U.S. Gov't, P.H.S.

PMID: 14570854 [PubMed - indexed for MEDLINE]

: A single set of low intensity resistance exercise immediately following high intensity resistance exercise stimulates growth hormone secretion in men.

Goto K, Sato K, Takamatsu K.

Doctoral Program in Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.

AIM: The purpose of the present study was to examine the effects of an additional set immediately following high intensity resistance exercise on growth hormone (GH) response. METHODS: Subjects (n=8) performed 4 resistance exercise protocols (bilateral knee extension exercise) on separate days. The protocols were categorized into 2 types of protocol, namely "Strength-up type (S-type)" and "Combination type (Combi-type)". The S-type was resistance exercise which consisted of 5 sets at 90% of 1 repetition maximum (RM) with 3-min rest periods between sets, whereas the Combi-type is a training protocol which adds an additional set (either 50% of 1 RM [C50-type], 70% of 1 RM [C70-type] or 90% of 1 RM [C90-type]) to the S-type. Serum GH concentration and blood lactate concentration were determined pre-exercise and at 0-60 min postexercise. Relative changes in thigh girth and maximal unilateral isometric strength were determined pre-exercise and immediately postexercise. RESULTS: The increasing values of GH concentration (DGH) in the S-type was the lowest of all protocols. On the other hand, DGH in the C50-type showed a significantly (p<0.05) higher increase than in the S-type and C90-type, and a relatively higher increase than in the C70-type. CONCLUSION: These results suggests that a high intensity, low volume training protocol to induce neural adaptation resulted in little GH response, but GH secretion was increased by performing a single set of low intensity resistance exercise at the end of a series of high intensity resistance sets.

PMID: 12853908 [PubMed - indexed for MEDLINE]

7: Scand J Med Sci Sports. 2003 Apr;13(2):88-97.

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Recent advances in the understanding of the repeated bout effect: the protective effect against muscle damage from a single bout of eccentric exercise.

McHugh MP.

The Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY, USA. mchugh@nismat.org

The repeated bout effect refers to the adaptation whereby a single bout of eccentric exercise protects against muscle damage from subsequent eccentric bouts. While the mechanism for this adaptation is poorly understood there have been significant recent advances in the understanding of this phenomenon. The purpose of this review is to provide an update on previously proposed theories and address new theories that have been advanced. The potential adaptations have been categorized as neural, mechanical and cellular. There is some evidence to suggest that the repeated bout effect is associated with a shift toward greater recruitment of slow twitch motor units. However, the repeated bout effect has been demonstrated with electrically stimulated contractions, indicating that a peripheral, non-neural adaptation predominates. With respect to mechanical adaptations there is evidence that both dynamic and passive muscle stiffness increase with eccentric training but there are no studies on passive or dynamic stiffness adaptations to a single eccentric bout. The role of the cytoskeleton in regulating dynamic stiffness is a possible area for future research. With respect to cellular adaptations there is evidence of longitudinal addition of sarcomeres and adaptations in the inflammatory response following an initial bout of eccentric exercise. Addition of sarcomeres is thought to reduce sarcomere strain during eccentric contractions thereby avoiding sarcomere disruption. Inflammatory adaptations are thought to limit the proliferation of damage that typically occurs in the days following eccentric exercise. In conclusion, there have been significant advances in the understanding of the repeated bout effect, however, a unified theory explaining the mechanism or mechanisms for this protective adaptation remains elusive.

Publication Types:

Review

PMID: 12641640 [PubMed - indexed for MEDLINE]

8: Sports Med. 2000 Dec;30(6):385-94.

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A proposed model for examining the interference phenomenon between concurrent aerobic and strength training.

Docherty D, Sporer B.

School of Physical Education, University of Victoria, British Columbia, Canada. docherty@uvic.ca

A review of the current research on the interference phenomenon between concurrent aerobic and strength training indicates modest support for the model proposed in this article. However, it is clear that without a systematic approach to the investigation of the phenomenon there is lack of control and manipulation of the independent variables, which makes it difficult to test the validity of the model. To enhance the understanding of the interference phenomenon, it is important that researchers are precise and deliberate in their choice of training protocols. Clear definition of the specific training objectives for strength (muscle hypertrophy or neural adaptation) and aerobic power (maximal aerobic power or anaerobic threshold) are required. In addition, researchers should equate training volumes as much as possible for all groups. Care needs to be exercised to avoid overtraining individuals. There should be adequate recovery and regeneration between the concurrent training sessions as well as during the training cycle. The model should be initially tested by maintaining the same protocols throughout the duration of the study. However, it is becoming common practice to use a periodised approach in a training mesocycle in which there is a shift from high volume and moderate intensity training to tower volume and higher intensity. The model should be evaluated in the context of a periodised mesocycle provided the investigators are sensitive to the potential impact of the loading parameters on the interference phenomenon. It may be that the periodised approach is one way of maintaining the training stimulus and minimising the amount of interference. The effects of gender, training status, duration and frequency of training, and the mode of training need to be regarded as potential factors effecting the training response when investigating the interference phenomenon. Other experimental design factors such as unilateral limb training or training the upper body for one attribute and the lower body for another attribute, may help establish the validity of the model.

Publication Types:

Review

PMID: 11132121 [PubMed - indexed for MEDLINE]

9: Eur J Appl Physiol. 2000 Sep;83(1):51-62.

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Neuromuscular adaptation during prolonged strength training, detraining and re-strength-training in middle-aged and elderly people.

Häkkinen K, Alen M, Kallinen M, Newton RU, Kraemer WJ.

Neuromuscular Research Centre and Department of Biology of Physical Activity, University of Jyväskylä, Finland. Hakkinen@Maila.jyu.fi

Effects of a 24-week strength training performed twice weekly (24 ST) (combined with explosive exercises) followed by either a 3-week detraining (3 DT) and a 21-week re-strength-training (21 RST) (experiment A) or by a 24-week detraining (24 DT) (experiment B) on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris, maximal isometric and one repetition maximum (1-RM) strength and jumping (J) and walking (W) performances were examined. A group of middle-aged (M, 37-44 years, n = 12) and elderly (E, 62-77, n = 10) and another group of M (35-45, n = 7) and E (63-78, n = 7) served as subjects. In experiment A, the 1-RM increased substantially during 24 ST in M (27%, P<0.001) and E (29%, P<0.001) and in experiment B in M (29%, P<0.001) and E (23%, P<0.01). During 21 RST the 1-RM was increased by 5% at week 48 (P<0.01) in M and 3% at week 41 in E (n.s., but P<0.05 at week 34). In experiment A the integrated electromyogram (IEMG) of the vastus muscles in the 1-RM increased during 24 ST in both M (P<0.05) and E (P<0.001) and during 21 RST in M for the right (P<0.05) and in E for both legs (P<0.05). The biceps femoris co-activation during the 1-RM leg extension decreased during the first 8-week training in M (from 29+/-5% to 25+/-3%, n.s.) and especially in E (from 41+/-11% to 32+/-9%, P<0.05). The CSA increased by 7% in M (P<0.05) and by 7% in E (P<0.001), and by 7% (n.s.) in M and by 3% in E (n.s.) during 24 ST periods. Increases of 18% (P<0.001) and 12% (P<0.05) in M and 22% (P<0.001) and 26% (P<0.05) in E occurred in J. W speed increased (P<0.05) in both age groups. The only decrease during 3 DT was in maximal isometric force in M by 6% (P<0.05) and by 4% (n.s.) in E. During 24 DT the CSA decreased in both age groups (P<0.01), the 1-RM decreased by 6% (P<0.05) in M and by 4% (P<0.05) in E and isometric force by 12% (P<0.001) in M and by 9% (P<0.05) in E, respectively, while J and W remained unaltered. The strength gains were accompanied by increased maximal voluntary neural activation of the agonists in both age groups with reduced antagonist co-activation in the elderly during the initial training phases. Neural adaptation seemed to play a greater role than muscle hypertrophy. Short-term detraining led to only minor changes, while prolonged detraining resulted in muscle atrophy and decreased voluntary strength, but explosive jumping and walking actions in both age groups appeared to remain elevated for quite a long time by compensatory types of physical activities when performed on a regular basis.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 11072774 [PubMed - indexed for MEDLINE]

: Plasma catecholamine responses and neural adaptation during short-term resistance training.

Pullinen T, Huttunen P, Komi PV.

Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväkylä, Finland. tpulline@pallo.jyu.fi

Low exercise-induced plasma adrenaline (A) responses have been reported in resistance-trained individuals. In the study reported here, we investigated the interaction between strength gain and neural adaptation of the muscles, and the plasma A response in eight healthy men during a short-term resistance-training period. The subjects performed 5 resistance exercises (E1-E5), consisting of 6 sets of 12 bilateral leg extensions performed at a 50% load, and with 2 days rest in between. Average electromyographic (EMG) signal amplitude was recorded before and after the exercises, from the knee extensor muscles in isometric maximal voluntary contraction (MVC) as well as during the exercises (aEMGmax and aEMGexerc, respectively). Total oxygen consumed during the exercises (VO2tot) was also measured. All of the exercises were exhaustive and caused significant decreases in MVC (34-36%, P < 0.001). As expected, the concentric one-repetition maximum (1-RM), MVC and aEMGmax were all higher before the last exercise (E5) than before the first exercise (E1; 7, 9 and 19%, respectively, P < 0.05). In addition, in E5 the aEMGexerc:load and VO2tot:load ratios were lower than in E1 (-5 and -14%, P < 0.05), indicating enhanced efficiency of the muscle contractions, However, the post-exercise plasma noradrenaline (NA) and A were not different in these two exercises [mean (SD) 10.2 (3.8) nmol x l(-1) vs 11.3 (6.0) nmol x l(-1), ns, and 1.2 (1.0) nmol x l(-1) vs 1.9 (1.1) nmol x l(-1), ns, respectively]. However, although NA increased similarly in every exercise (P < 0.01), the increase in A reached the level of statistical significance only in E1 (P < 0.05). The post-exercise A was also already lower in E2 [0.7 (0.7) nmol x l(-1), P < 0.05) than in E1, despite the higher post-exercise blood lactate concentration than in the other exercises [9.4 (1.1) mmol x l(-1), P < 0.05]. Thus, the results suggest that the observed attenuation in the A response can not be explained by reduced exercise-induced strain due to the strength gain and neural adaptation of the muscles. Correlation analysis actually revealed that those individuals who had the highest strength gain during the training period even tended to have an increased post-exercise A concentration in the last exercise as compared to first one (r = 0.76, P < 0.05).

PMID: 10879445 [PubMed - indexed for MEDLINE]

11: Sports Med. 1999 Mar;27(3):157-70.

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Exercise-induced muscle damage and potential mechanisms for the repeated bout effect.

McHugh MP, Connolly DA, Eston RG, Gleim GW.

School of Sport, Health and Physical Education Sciences, University of Wales, Bangor, Gwynedd, Wales. mchugh@nismat.org

Unfamiliar, predominantly eccentric exercise, frequently results in muscle damage. A repeated bout of similar eccentric exercise results in less damage and is referred to as the 'repeated bout effect'. Despite numerous studies that have clearly demonstrated the repeated bout effect, there is little consensus as to the actual mechanism. In general, the adaptation has been attributed to neural, connective tissue or cellular adaptations. Other possible mechanisms include, adaptation in excitation-contraction coupling or adaptation in the inflammatory response. The 'neural theory' predicts that the initial damage is a result of high stress on a relatively small number of active fast-twitch fibres. For the repeated bout, an increase in motor unit activation and/or a shift to slow-twitch fibre activation distributes the contractile stress over a larger number of active fibres. Although eccentric training results in marked increases in motor unit activation, specific adaptations to a single bout of eccentric exercise have not been examined. The 'connective tissue theory' predicts that muscle damage occurs when the noncontractile connective tissue elements are disrupted and myofibrillar integrity is lost. Indirect evidence suggests that remodelling of the intermediate filaments and/or increased intramuscular connective tissue are responsible for the repeated bout effect. The 'cellular theory' predicts that muscle damage is the result of irreversible sarcomere strain during eccentric contractions. Sarcomere lengths are thought to be highly non-uniform during eccentric contractions, with some sarcomeres stretched beyond myofilament overlap. Loss of contractile integrity results in sarcomere strain and is seen as the initial stage of damage. Some data suggest that an increase in the number of sarcomeres connected in series, following an initial bout, reduces sarcomere strain during a repeated bout and limits the subsequent damage. It is unlikely that one theory can explain all of the various observations of the repeated bout effect found in the literature. That the phenomenon occurs in electrically stimulated contractions in an animal model precludes an exclusive neural adaptation. Connective tissue and cellular adaptations are unlikely explanations when the repeated bout effect is demonstrated prior to full recovery, and when the fact that the initial bout does not have to cause appreciable damage in order to provide a protective effect is considered. It is possible that the repeated bout effect occurs through the interaction of various neural, connective tissue and cellular factors that are dependent on the particulars of the eccentric exercise bout and the specific muscle groups involved.

Publication Types:

Review

PMID: 10222539 [PubMed - indexed for MEDLINE]

12: Eur J Appl Physiol Occup Physiol. 1998;77(1-2):170-5.

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A comparison of strength and muscle mass increases during resistance training in young women.

Chilibeck PD, Calder AW, Sale DG, Webber CE.

Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.

Strength gains with resistance training are due to muscle hypertrophy and nervous system adaptations. The contribution of either factor may be related to the complexity of the exercise task used during training. The purpose of this investigation was to measure the degree to which muscle hypertrophy contributes to gains in strength during exercises of varying complexity. Nineteen young women resistance trained twice a week for 20 weeks, performing exercises designed to provide whole-body training. The lean mass of the trunk, legs and arms was measured by dual energy x-ray absorptiometry and compared to strength gains (measured as the 1-repetition maximum) in bench press, leg press and arm curl exercises, pre-, mid- (10 weeks) and post-training. No changes were found in a control group of ten women. For the exercise group, increases in bench press, leg press and arm curl strength were significant from pre- to mid-, and from mid- to post-training (P < 0.05). In contrast, increases in the lean mass of the body segments used in these exercises followed a different pattern. Increases in the lean mass of the arms were significant from pre- to mid-training, while increases in the lean mass of the trunk and legs were delayed and significant from mid- to post-training only (P < 0.05). It is concluded that a more prolonged neural adaptation related to the more complex bench and leg press movements may have delayed hypertrophy in the trunk and legs. With the simpler arm curl exercise, early gains in strength were accompanied by muscle hypertrophy and, presumably, a faster neural adaptation.

Publication Types:

PMID: 9459538 [PubMed - indexed for MEDLINE]

13: J Orthop Sports Phys Ther. 1998 Jan;27(1):3-8.

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Weight training of the thigh muscles using closed vs. open kinetic chain exercises: a comparison of performance enhancement.

Augustsson J, Esko A, Thomeé R, Svantesson U.

Department of Rehabilitation Medicine, Göteborg University, Sweden.

Resistance training is commonly used in sports for prevention of injuries and in rehabilitation. The purpose of this study was to compare closed vs. open kinetic chain weight training of the thigh muscles and to determine which mode resulted in the greatest performance enhancement. Twenty-four healthy subjects were randomized into a barbell squat or a knee extension and hip adduction variable resistance weight machine group and performed maximal, progressive weight training twice a week for 6 weeks. All subjects were tested prior to training and at the completion of the training period. A barbell squat 3-repetition maximum, an isokinetic knee extension 1-repetition maximum, and a vertical jump test were used to monitor effects of training. Significant improvements were seen in both groups in the barbell squat 3-repetition maximum test. The closed kinetic chain group improved 23 kg (31%), which was significantly more than the 12 kg (13%) seen in the open kinetic chain group. In the vertical jump test, the closed kinetic chain group improved significantly, 5 cm (10%), while no significant changes were seen in the open kinetic chain group. A large increase of training load was observed in both subject groups; however, improvements in isotonic strength did not transfer to the isokinetic knee extension test. The results may be explained by neural adaptation, weight training mode, and specificity of tests.

Publication Types:

PMID: 9440034 [PubMed - indexed for MEDLINE]

14: Clin Physiol. 1997 May;17(3):311-24.

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Dynamic muscle strength alterations to detraining and retraining in elderly men.

Taaffe DR, Marcus R.

Musculoskeletal Research Laboratory, Veterans Affairs Medical Center, Palo Alto, California, USA.

To investigate the effects of cessation and subsequent resumption of training on muscle strength in elderly men, 11 men (aged 65-77 years), just completing a 24-week randomized controlled trial of recombinant human growth hormone (rhGH) and resistance exercise (rhGH, n = 6; placebo, n = 5), detrained for 12 weeks and subsequently retrained for 8 weeks. During the detraining and retraining phase, subjects did not receive rhGH. The resistance programme included three sets of eight repetitions at 75% of one-repetition maximum (1-RM), three times per week, for 10 upper and lower body exercises. Dynamic muscle strength was assessed by the 1-RM method every 2 weeks for 44 weeks. Needle biopsies of vastus lateralis muscle were obtained from seven men. Muscle strength increased during initial training by 40.4 +/- 5.5% (mean +/- SEM), ranging from 26.0 +/- 5.0 to 83.9 +/- 15.6%, depending on muscle group. Increased strength was accompanied by hypertrophy (P < 0.05) of type I (17.4 +/- 4.1%) and II (25.8 +/- 12.4%) muscle fibres. Of initial strength gains, only 29.9 +/- 5.2% was lost with detraining. However, type I and II fibre cross-sectional area reverted to pretraining values. After 8 weeks of retraining, muscle strength returned to trained values, but without a significant change in fibre morphology. The results indicate that elderly men lose some muscle strength following short-term detraining, but that only a brief period of retraining suffices to regain maximal strength. Reversal of fibre cross-sectional area with detraining, and only modest improvement with retraining, suggests that much of the retention in strength with detraining and reacquisition of lost strength with retraining reflects neural adaptation.

Publication Types:

PMID: 9171971 [PubMed - indexed for MEDLINE]

15: J Appl Physiol. 1996 Mar;80(3):765-72.

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Adaptive responses to muscle lengthening and shortening in humans.

Hortobágyi T, Hill JP, Houmard JA, Fraser DD, Lambert NJ, Israel RG.

Biomechanics Laboratory and Department of Medicine and Physical Therapy, East Carolina University, Greenville, North Carolina 27858, USA.

We tested the hypothesis that exercise training with maximal eccentric (lengthening) muscle actions results in greater gains in muscle strength and size than training with concentric (shortening) actions. Changes in muscle strength, muscle fiber size, and surface electromyographic (EMG) activity of the quadriceps muscle were compared after 36 sessions of isokinetic concentric (n = 8) or eccentric (n = 7) exercise training over 12 wk with use of a one-leg model. Eccentric training increased eccentric strength 3.5 times more (pre/post 46%, P < 0.05) than concentric training increased concentric strength (pre/post 13%). Eccentric training increased concentric strength and concentric training increased eccentric strength by about the same magnitude (5 and 10%, respectively, P > 0.05). Eccentric training increased EMG activity seven times more during eccentric testing (pre/post 86%, P < 0.05) than concentric training increased EMG activity during concentric testing (pre/post 12%). Eccentric training increased the EMG activity measured during concentric tests and concentric training increased the EMG activity measured during eccentric tests by about the same magnitude (8 and 11%, respectively, P > 0.05). Type I muscle fiber percentages did not change significantly, but type IIa fibers increased and type IIb fibers decreased significantly (P < 0.05) in both training groups. Type I fiber areas did not change significantly (P > 0.05), but type II fiber area increased approximately 10 times more (P < 0.05) in the eccentric than in the concentric group. It is concluded that adaptations to training with maximal eccentric contractions are specific to eccentric muscle actions that are associated with greater neural adaptation and muscle hypertrophy than concentric exercise.

Publication Types:

PMID: 8964735 [PubMed - indexed for MEDLINE]

16: Aviat Space Environ Med. 1995 Mar;66(3):251-5.

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Training effects of electrically induced dynamic contractions in human quadriceps muscle.

Kim CK, Takala TE, Seger J, Karpakka J.

Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden.

The effects of electrically induced dynamic muscle contractions on muscle endurance, strength, morphology and enzymatic adaptation were studied in seven male physical education students. The training program consisted of electrically induced one-leg extensions on a modified Krogh cycle with a 30-Watt (W) load for 60 min, 3 times a week for 4 weeks. Muscle fiber type composition was unchanged, but diffusional capacity was increased after electromyostimulation training. The endurance capacity in the trained leg increased by 82% (p < 0.01), but there were no significant changes in citrate synthase, phosphofructokinase activities, and carbonic anhydrase III and myoglobin contents, suggesting that neural adaptation and learning were more important factors for the increased endurance capacity than enzymatic adaptation. Prolyl 4-hydroxylase activity, a marker of collagen biosynthesis, increased 3-fold (p < 0.01) as a result of the training. This could be due to muscle damage caused by electrically induced muscle contractions. In conclusion, electrically induced dynamic muscle contractions can increase muscle endurance without clear concominant changes in muscle morphologic and enzymatic adaptation. Increased prolyl 4-hydroxylase activity could suggest muscle damage caused by electrically induced muscle contractions.

Publication Types:

PMID: 7661836 [PubMed - indexed for MEDLINE]

17: Acta Physiol Scand. 1990 Sep;140(1):31-9.

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Effects of eccentric and concentric muscle actions in resistance training.

Colliander EB, Tesch PA.

Department of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.

The adaptive responses to two different resistance training regimens were compared. Healthy males performed five sets of either 12 maximum bilateral concentric (Grp CON; n = 11) or six pairs of maximum bilateral eccentric and concentric (Grp ECCON; n = 11) quadriceps muscle actions three times per week for 12 weeks. Uni- and bilateral eccentric and concentric peak torque at various angular velocities, vertical jump height and three-repetition maximum half-squat were measured before and after training. Muscle biopsies were obtained from m. vastus lateralis and analysed for fibre type composition and area using histochemical techniques. In contrast to a control group (n = 7), performing no training, Grps CON and ECCON demonstrated marked increases (P less than 0.05) in overall eccentric (19 and 37% respectively) and concentric (15 and 26% respectively) peak torques. Grp ECCON, however, showed greater (P less than 0.05) increases in peak torque, vertical jump height and three repetition maximum than Grp CON. The 7% increases in slow-twitch fibre area in Grps CON and ECCON and in fast-twitch fibre area in Grp CON were non-significant. This study suggests that increases in peak torque and strength-related performance parameters were greater following a programme consisting of maximum concentric and eccentric muscle actions than resistance training using concentric muscle actions only. Because increases in muscle fibre areas were small it is also suggested that the increased muscle strength shown subsequent to short-term accommodated resistance training is mainly due to neural adaptation.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 2275403 [PubMed - indexed for MEDLINE]

18: Med Sci Sports Exerc. 1988 Oct;20(5 Suppl):S135-45.

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Neural adaptation to resistance training.

Sale DG.

Department of Physical Education, McMaster University, Hamilton, Ontario, Canada.

Strength performance depends not only on the quantity and quality of the involved muscles, but also upon the ability of the nervous system to appropriately activate the muscles. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime movers in specific movements and to better coordinate the activation of all relevant muscles, thereby effecting a greater net force in the intended direction of movement. The evidence indicating neural adaptation is reviewed. Electromyographic studies have provided the most direct evidence. They have shown that increases in peak force and rate of force development are associated with increased activation of prime mover muscles. Possible reflex adaptations related to high stretch loads in jumping and rapid reciprocal movements have also been revealed. Other studies, including those that demonstrate the "cross-training" effect and specificity of training, provide further evidence of neural adaptation. The possible mechanisms of neural adaptation are discussed in relation to motor unit recruitment and firing patterns. The relative roles of neural and muscular adaptation in short- and long-term strength training are evaluated.

Publication Types:

Review

PMID: 3057313 [PubMed - indexed for MEDLINE]

1: J Physiol. 2002 Oct 15;544(Pt 2):641-52.

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The sites of neural adaptation induced by resistance training in humans.

Carroll TJ, Riek S, Carson RG.

Perception and Motor Systems Laboratory, The School of Human Movement Studies, The University of Queensland, Brisbane, Queensland 4072, Australia. tcarroll@ualberta.ca

Although it has long been supposed that resistance training causes adaptive changes in the CNS, the sites and nature of these adaptations have not previously been identified. In order to determine whether the neural adaptations to resistance training occur to a greater extent at cortical or subcortical sites in the CNS, we compared the effects of resistance training on the electromyographic (EMG) responses to transcranial magnetic (TMS) and electrical (TES) stimulation. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle of 16 individuals before and after 4 weeks of resistance training for the index finger abductors (n = 8), or training involving finger abduction-adduction without external resistance (n = 8). TMS was delivered at rest at intensities from 5 % below the passive threshold to the maximal output of the stimulator. TMS and TES were also delivered at the active threshold intensity while the participants exerted torques ranging from 5 to 60 % of their maximum voluntary contraction (MVC) torque. The average latency of MEPs elicited by TES was significantly shorter than that of TMS MEPs (TES latency = 21.5 +/- 1.4 ms; TMS latency = 23.4 +/- 1.4 ms; P < 0.05), which indicates that the site of activation differed between the two forms of stimulation. Training resulted in a significant increase in MVC torque for the resistance-training group, but not the control group. There were no statistically significant changes in the corticospinal properties measured at rest for either group. For the active trials involving both TMS and TES, however, the slope of the relationship between MEP size and the torque exerted was significantly lower after training for the resistance-training group (P < 0.05). Thus, for a specific level of muscle activity, the magnitude of the EMG responses to both forms of transcranial stimulation were smaller following resistance training. These results suggest that resistance training changes the functional properties of spinal cord circuitry in humans, but does not substantially affect the organisation of the motor cortex.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 12381833 [PubMed - indexed for MEDLINE]

PMCID: PMC2290590

: Mechanomyographic response to transcranial magnetic stimulation from biceps brachii and during transcutaneous electrical nerve stimulation on extensor carpi radialis.

Reza MF, Ikoma K, Chuma T, Mano Y.

Department of Rehabilitation and Physical Medicine, Hokkaido University Graduate School of Medicine, N15 W7, Sapporo 060-8638, Japan.

Transcranial magnetic stimulation (TMS) elicits short latency excitatory responses in the target muscles, termed motor evoked potential (MEP). When TMS is delivered during a voluntary contraction, the MEP is followed by a period of silence called silent period (SP). These MEP parameters are in general recordable by electromyography (EMG). Mechanomyography (MMG) on the other hand is the mechanical counterpart of EMG. Thus, this study has been conducted to observe whether the MEP parameters from MMG signals showed similar trait of EMG recordings. Five normal healthy male subjects were included in this study. The subjects were required to perform right biceps brachii muscles contraction at diverse graded of load level at 5, 10, 20, 30, 40, 60, and 100% maximum voluntary contraction (MVC). MEPs by single pulse TMS on left hemisphere were obtained from both EMG electrode and MMG accelerometer at rest and at different levels of predetermined load level. MEP amplitude and area obtained both from EMG and MMG record were increased with the increase of muscle contraction with a maximum of 60% MVC. With increasing the level of contraction there was a shortening of onset latency and decreasing in the length of silent period in both EMG and MMG signals. We also recorded the EMG- and MMG-MEP from the right extensor carpi radialis muscle during transcutaneous electric nerve stimulation in order to observe neural changes in sensory stimulation from both EMG and MMG responses. The EMG-MEP was not visible in electrical artifact whereas it was obvious in MMG responses. In accordance with other study, this study showed that the voluntary contraction of biceps brachii muscle influenced the MEP parameter which are moreover obtainable by MMG even in electrical noise may provide insight for future study.

PMID: 16026847 [PubMed - indexed for MEDLINE]

3: J Appl Physiol. 2005 Oct;99(4):1558-68. Epub 2005 May 12.

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Motor skill training and strength training are associated with different plastic changes in the central nervous system.

Jensen JL, Marstrand PC, Nielsen JB.

Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark. j.b.nielsen@mfi.ku.dk

Changes in corticospinal excitability induced by 4 wk of heavy strength training or visuomotor skill learning were investigated in 24 healthy human subjects. Measurements of the input-output relation for biceps brachii motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation were obtained at rest and during voluntary contraction in the course of the training. The training paradigms induced specific changes in the motor performance capacity of the subjects. The strength training group increased maximal dynamic and isometric muscle strength by 31% (P < 0.001) and 12.5% (P = 0.045), respectively. The skill learning group improved skill performance significantly (P < 0.001). With one training bout, the only significant change in transcranial magnetic stimulation parameters was an increase in skill learning group maximal MEP level (MEP(max)) at rest (P = 0.02) for subjects performing skill training. With repeated skill training three times per week for 4 wk, MEP(max) increased and the minimal stimulation intensity required to elicit MEPs decreased significantly at rest and during contraction (P < 0.05). In contrast, MEP(max) and the slope of the input-output relation both decreased significantly at rest but not during contraction in the strength-trained subjects (P < or = 0.01). No significant changes were observed in a control group. A significant correlation between changes in neurophysiological parameters and motor performance was observed for skill learning but not strength training. The data show that increased corticospinal excitability may develop over several weeks of skill training and indicate that these changes may be of importance for task acquisition. Because strength training was not accompanied by similar changes, the data suggest that different adaptive changes are involved in neural adaptation to strength training.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 15890749 [PubMed - indexed for MEDLINE]

4: Sports Med. 2006;36(2):133-49.

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Neural adaptations to resistive exercise: mechanisms and recommendations for training practices.

Gabriel DA, Kamen G, Frost G.

Department of Physical Education and Kinesiology, Brock University, St Catharines, Ontario, Canada. dgabriel@brocku.ca

It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation.An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated.There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation.Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force.Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity.The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.

Publication Types:

PMID: 16464122 [PubMed - indexed for MEDLINE]

5: J Neurosci. 2003 Nov 12;23(32):10224-30.

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Responses of human motoneurons to corticospinal stimulation during maximal voluntary contractions and ischemia.

Butler JE, Taylor JL, Gandevia SC.

Prince of Wales Medical Research Institute and University of New South Wales, Randwick, New South Wales, 2031 Australia.

The discharge frequency of human motoneurons declines during a sustained isometric maximal voluntary contraction (MVC) of elbow flexor muscles, but the cause is unresolved. We aimed to determine whether motoneurons were inhibited during a sustained fatiguing contraction of the elbow flexor muscles and whether this inhibition was caused by the discharge of group III and IV muscle afferents. Subjects performed brief MVCs before and after a fatiguing 2 min MVC. During maximal efforts, electromyographic responses recorded from the elbow flexor muscles were evoked by stimulation of the corticospinal tracts at the cervicomedullary level [cervicomedullary motor evoked potentials (CMEPs)] and by supramaximal stimulation over the brachial plexus (Mmax). This revealed a novel decrease in the size of the muscle response to corticospinal tract stimulation during fatigue. During the sustained MVCs, the size of CMEPs decreased to 81 +/- 15 and 78 +/- 15% of the control value for brachioradialis and biceps brachii, respectively (mean +/- SEM; n = 8). This recovered within 15 sec after the fatiguing contraction. In a second set of studies, input from group III and IV muscle afferents was prolonged after the end of the fatiguing contraction by holding the muscle ischemic with a cuff inflated above arterial pressure. Despite the maintained discharge of group III and IV afferents, the CMEPs again recovered within 15 sec of the end of the sustained contraction. These results show a diminished output of spinal motoneurons to stimulation of corticospinal tracts during a fatiguing MVC; however, the mechanisms responsible for this decline are not attributable to activity in group III and IV muscle afferents.

Publication Types:

PMID: 14614080 [PubMed - indexed for MEDLINE]

6: J Neurosci. 2006 May 3;26(18):4796-802.

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Fatigue-sensitive afferents inhibit extensor but not flexor motoneurons in humans.

Martin PG, Smith JL, Butler JE, Gandevia SC, Taylor JL.

Prince of Wales Medical Research Institute, University of New South Wales, Randwick, New South Wales 2031, Australia.

The role of group III and IV muscle afferents in controlling the output from human muscles is poorly understood. We investigated the effects of these afferents from homonymous or antagonist muscles on motoneuron pools innervating extensor and flexor muscles of the elbow. In study 1, subjects (n = 8) performed brief maximal voluntary contractions (MVCs) of elbow extensors before and after a 2 min MVC of the extensors. During MVCs, electromyographic responses from triceps were evoked by stimulation of the corticospinal tracts [cervicomedullary motor evoked potentials (CMEPs)]. The same subjects repeated the protocol, but input from fatigue-sensitive afferents was prolonged after the fatiguing contraction by maintained muscle ischemia. In study 2, CMEPs were evoked in triceps during brief extensor MVCs before and after a 2 min sustained flexor MVC (n = 7) or in biceps during brief flexor MVCs before and after a sustained extensor MVC (n = 7). Again, ischemia was maintained after the sustained contractions. During sustained MVCs of the extensors, CMEPs in triceps decreased by approximately 35%. Without muscle ischemia, CMEPs recovered within 15 s, but with maintained ischemia, they remained depressed (by approximately 28%; p < 0.001). CMEPs in triceps were also depressed (by approximately 20%; p < 0.001) after fatiguing flexor contractions, whereas CMEPs in biceps were facilitated (by approximately 25%; p < 0.001) after fatiguing extensor contractions. During fatigue, inputs from group III and IV muscle afferents from homonymous or antagonist muscles depress extensor motoneurons but facilitate flexor motoneurons. The more pronounced inhibitory influence of these afferents on extensors suggests that these muscles may require greater cortical drive to generate force during fatigue.

Publication Types:

PMID: 16672652 [PubMed - indexed for MEDLINE]

7: Exp Physiol. 2006 Jan;91(1):171-8. Epub 2005 Oct 6.

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Maximal motor unit firing rates during isometric resistance training in men.

Pucci AR, Griffin L, Cafarelli E.

School of Kinesiology and Health Science, York University, Toronto, ON, Canada.

This study measured changes in maximal voluntary contraction (MVC) force, percentage maximal activation, maximal surface EMG, M-wave amplitude and average motor unit firing rates during the initial 3 weeks of isometric resistance training of the quadriceps muscle. Ten men participated in a resistance training programme three times a week for 3 weeks and 10 men participated as a control group. In the training group, MVC increased by 35% (from 761 +/- 77 to 1031 +/- 78 N) by the end of the 3 weeks. There were no changes in mean motor unit firing rates during submaximal or maximal voluntary contractions of 50 (15.51 +/- 1.48 Hz), 75 (20.23 +/- 1.85 Hz) or 100% MVC (42.25 +/- 2.72 Hz) with isometric resistance training. There was also no change in maximal surface EMG relative to the M-wave amplitude. However, there was a small increase in maximal activation (from 95.7 +/- 1.83 to 98.44 +/- 0.66%) as measured by the twitch interpolation technique. There were no changes in any of the parameters measured in the control group. It is suggested that mechanisms other than increases in average motor unit firing rates contributed to the increase in maximal force output with resistance training. Such mechanisms may include a combination of increased motor unit recruitment, enhanced protein synthesis, and changes in motor unit synchronization and muscle activation patterns across the quadriceps synergy.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 16210447 [PubMed - indexed for MEDLINE]

8: J Appl Physiol. 2002 Oct;93(4):1318-26.

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Increased rate of force development and neural drive of human skeletal muscle following resistance training.

Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P.

Department of Neurophysiology, Institute of Medical Physiology, Bispebjerg Hospital, University of Copenhagen, DK-2200 Copenhagen, Denmark. p.aagaard@mfi.ku.dk

The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 12235031 [PubMed - indexed for MEDLINE]

9: Exp Brain Res. 2000 Jun;132(4):517-22.

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Post-exercise facilitation of compound muscle action potentials evoked by transcranial magnetic stimulation in healthy subjects.

Nørgaard P, Nielsen JF, Andersen H.

Department of Neurology, Aarhus University Hospital, Denmark.

Post-exercise facilitation (PEF) of motor evoked potentials (MEPs) was studied by transcranial magnetic stimulation in 15 healthy subjects following standardized and controlled isometric contraction of the biceps brachii muscle. PEF was highly dependent on the time delay (TD) from muscle relaxation to delivery of the magnetic stimulus and only to a minor degree on the duration of the maintained muscular contraction of 2, 4, and 6 s. In addition, PEF was unaffected by the contraction levels of 25%, 50%, and 100% of maximal voluntary contraction (MVC). There was a linear relationship between the log amplitude of the post-exercise MEPs and the TD. The time point at which PEF had vanished was calculated to be 15.2 s. In order to challenge the question whether segmental and/or suprasegmental mechanisms are primarily responsible for PEF, MEPs and H-reflexes were recorded from the soleus muscle following a sustained plantar flexion at the ankle joint in three healthy subjects. PEF of MEPs was present at a TD of 1000 ms following a sustained contraction of 6 s at a level of 50% of MVC. It was accompanied by a pronounced decrease in the soleus H-reflex amplitude at a TD of 1000 ms.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 10912832 [PubMed - indexed for MEDLINE]

10: J Appl Physiol. 2002 Jun;92(6):2309-18.

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Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses.

Aagaard P, Simonsen EB, Andersen JL, Magnusson P, Dyhre-Poulsen P.

Department of Neurophysiology, Institute of Medical Physiology, Denmark. p.aagaard@mfi.ku.dk

Combined V-wave and Hoffmann (H) reflex measurements were performed during maximal muscle contraction to examine the neural adaptation mechanisms induced by resistance training. The H-reflex can be used to assess the excitability of spinal alpha-motoneurons, while also reflecting transmission efficiency (i.e., presynaptic inhibition) in Ia afferent synapses. Furthermore, the V-wave reflects the overall magnitude of efferent motor output from the alpha-motoneuron pool because of activation from descending central pathways. Fourteen male subjects participated in 14 wk of resistance training that involved heavy weight-lifting exercises for the muscles of the leg. Evoked V-wave, H-reflex, and maximal M-wave (M(max)) responses were recorded before and after training in the soleus muscle during maximal isometric ramp contractions. Maximal isometric, concentric, and eccentric muscle strength was measured by use of isokinetic dynamometry. V-wave amplitude increased approximately 50% with training (P < 0.01) from 3.19 +/- 0.43 to 4.86 +/- 0.43 mV, or from 0.308 +/- 0.048 to 0.478 +/- 0.034 when expressed relative to M(max) (+/- SE). H-reflex amplitude increased approximately 20% (P < 0.05) from 5.37 +/- 0.41 to 6.24 +/- 0.49 mV, or from 0.514 +/- 0.032 to 0.609 +/- 0.025 when normalized to M(max). In contrast, resting H-reflex amplitude remained unchanged with training (0.503 +/- 0.059 vs. 0.499 +/- 0.063). Likewise, no change occurred in M(max) (10.78 +/- 0.86 vs. 10.21 +/- 0.66 mV). Maximal muscle strength increased 23-30% (P < 0.05). In conclusion, increases in evoked V-wave and H-reflex responses were observed during maximal muscle contraction after resistance training. Collectively, the present data suggest that the increase in motoneuronal output induced by resistance training may comprise both supraspinal and spinal adaptation mechanisms (i.e., increased central motor drive, elevated motoneuron excitability, reduced presynaptic inhibition).

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 12015341 [PubMed - indexed for MEDLINE]

11: Exp Brain Res. 2004 Nov;159(2):225-38. Epub 2004 Jul 7.

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Transfer of resistance training to enhance rapid coordinated force production by older adults.

Barry BK, Carson RG.

Perception and Motor Systems Laboratory, School of Human Movement Studies, The University of Queensland, St Lucia, Queensland 4072, Australia. benjamin.barry@colorado.edu

The purpose of this study was to examine the capacity of resistance training to enhance the rapid and coordinated production of force by older people. Thirty adults (> or =60 years) completed a visually guided aiming task that required the generation of isometric torque in 2 df about the elbow prior to and following a 4-week training period. Groups of six participants were allocated to two progressive (40-100% maximal voluntary contraction (MVC)) resistance-training (PRT) groups, to two constant low-load (10% MVC) training groups (CLO) and to one no-training control group. Training movements required the generation of either combined flexion and supination (FLESUP), or combined extension and supination (EXTSUP). In response to training, target acquisition times in the aiming task decreased for all groups; however, both the nature of the training load and the training movement influenced the pattern and magnitude of improvements (EXTSUP_CLO: 36%, FLESUP_PRT 26%, EXTSUP_PRT 22%, FLESUP_CLO 20%, CONTROL 15%). For one group that trained with progressively increasing loads, there arose a subsequent decrease in performance in one condition of the transfer task. For each group, these adaptations were accompanied by systematic changes in the coordination of muscles about the elbow joint, particularly the biceps brachii.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 15241574 [PubMed - indexed for MEDLINE]

12: Muscle Nerve. 2000 Mar;23(3):376-84.

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Evidence of inability to fully activate human limb muscle.

Yue GH, Ranganathan VK, Siemionow V, Liu JZ, Sahgal V.

Department of Biomedical Engineering/ND20, The Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA. yue@bme.ri.ccf.org

The purpose of this study was to determine whether muscle activation level estimated by twitch interpolation technique was different when an electrical stimulus was applied during a dynamic force (DF; force rising) task from that when the stimulus was applied during a static force (SF; constant force) task. Fourteen subjects performed voluntary SF and DF contractions involving isometric elbow flexion at seven voluntary force levels. At each level, the electrical stimulation was applied to the surface of the biceps brachii muscle when the force was steady (SF task) and when the force was rising (DF task). The voluntary activation level of the biceps brachii muscle during the SF maximal voluntary contraction (MVC) was 98.5% and that during the DF MVC task was significantly lower (94.5%; P < 0.05). The motoneurons and/or muscle fibers may become more excitable during the DF task so that the same stimulus can recruit those that are otherwise less excitable during the SF task. Copyright 2000 John Wiley & Sons, Inc.

Publication Types:

PMID: 10679714 [PubMed - indexed for MEDLINE]

13: J Appl Physiol. 2006 Oct;101(4):1036-44. Epub 2006 May 25.

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Comment in:

J Appl Physiol. 2006 Oct;101(4):1015-6.

Supraspinal fatigue does not explain the sex difference in muscle fatigue of maximal contractions.

Hunter SK, Butler JE, Todd G, Gandevia SC, Taylor JL.

Exercise Science Program, Department of Physical Therapy, PO Box 1881, Marquette University, Milwaukee, WI 53201, USA. Sandra.Hunter@marquette.edu

Young women are less fatigable than young men for maximal and submaximal contractions, but the contribution of supraspinal fatigue to the sex difference is not known. This study used cortical stimulation to compare the magnitude of supraspinal fatigue during sustained isometric maximal voluntary contractions (MVCs) performed with the elbow flexor muscles of young men and women. Eight women (25.6 +/- 3.6 yr, mean +/- SD) and 9 men (25.4 +/- 3.8 yr) performed six sustained MVCs (22-s duration each, separated by 10 s). Before the fatiguing contractions, the men were stronger than the women (75.9 +/- 9.2 vs. 42.7 +/- 8.0 N.m; P < 0.05) in control MVCs. Voluntary activation measured with cortical stimulation before fatigue was similar for the men and women during the final control MVC (95.7 +/- 3.0 vs. 93.3 +/- 3.6%; P > 0.05) and at the start of the fatiguing task (P > 0.05). By the end of the six sustained fatiguing MVCs, the men exhibited greater absolute and relative reductions in torque (65 +/- 3% of initial MVC) than the women (52 +/- 9%; P < 0.05). The increments in torque (superimposed twitch) generated by motor cortex stimulation during each 22-s maximal effort increased with fatigue (P < 0.05). Superimposed twitches were similar for men and women throughout the fatiguing task (5.5 +/- 4.1 vs. 7.3 +/- 4.7%; P > 0.05), as well as in the last sustained contraction (7.8 +/- 5.9 vs. 10.5 +/- 5.5%) and in brief recovery MVCs. Voluntary activation determined using an estimated control twitch was similar for the men and women at the start of the sustained maximal contractions (91.4 +/- 7.4 vs. 90.4 +/- 6.8%, n = 13) and end of the sixth contraction (77.2 +/- 13.3% vs. 73.1 +/- 19.6%, n = 10). The increase in the area of the motor-evoked potential and duration of the silent period did not differ for men and women during the fatiguing task. However, estimated resting twitch amplitude and the peak rates of muscle relaxation showed greater relative reductions at the end of the fatiguing task for the men than the women. These results indicate that the sex difference in fatigue of the elbow flexor muscles is not explained by a difference in supraspinal fatigue in men and women but is largely due to a sex difference of mechanisms located within the elbow flexor muscles.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 16728525 [PubMed - indexed for MEDLINE]

14: Can J Appl Physiol. 2005 Jun;30(3):328-40.

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Resistance training: cortical, spinal, and motor unit adaptations.

Griffin L, Cafarelli E.

Dept. of Kinesiology and Health Education, University of Texas, Austin, TX 78712, USA.

During the first few weeks of isometric resistance training there is an increase in maximal muscle force output that cannot be accounted for by muscle hypertrophy. Early on, researchers postulated the existence of neural adaptations to training primarily through the use of surface electromyographic recordings. More recent evidence also suggests that increased excitation may occur at the cortical levels following short-term resistance training. Alterations in synergistic activation and reductions in antagonist activation are neural factors that have been identified as changing during the early stages of resistance training which could contribute to maximal force generation. Neural adaptations that occur during the ramp-up phase of isometric contraction include decreases in motor unit recruitment thresholds, increased motor unit discharge rates, and increases in double discharges. An increase in the maximal rate of force development also occurs during the early stages of resistance training, but whether the neural mechanisms associated with the increase in the rate of rise are also associated with the increase in maximal force has not been elucidated. More work is needed to examine the integration of changes in cortical and spinal excitability with single motor unit firing patterns during this simple form of exercise before we can extend our understanding to different types of training.

Publication Types:

Review

PMID: 16129897 [PubMed - indexed for MEDLINE]

15: Clin Physiol Funct Imaging. 2007 Mar;27(2):91-100.

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PMID: 17309529 [PubMed - indexed for MEDLINE]

16: Eur J Appl Physiol. 2002 Feb;86(4):287-94.

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Cross education of muscular strength during unilateral resistance training and detraining.

Shima N, Ishida K, Katayama K, Morotome Y, Sato Y, Miyamura M.

Research Center of Health, Physical Fitness and Sports, Nagoya University, Japan. nshima@med.nagoya-u.ac.jp

The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 day-s x week(-1) for 6 weeks using 3 sets of 10-12 repetitions at 70-75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P < 0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 11990741 [PubMed - indexed for MEDLINE]

17: Exerc Sport Sci Rev. 2003 Apr;31(2):61-7.

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Training-induced changes in neural function.

Aagaard P.

Department of Neurophysiology, Institute of Medical Physiology, Panum Institute, Copenhagen, Denmark. p.aagaard@mfi.ku.dk

Adaptive changes can occur in the nervous system in response to training. Electromyography studies have indicated adaptation mechanisms that may contribute to an increased efferent neuronal outflow with training, including increases in maximal firing frequency, increased excitability and decreased presynaptic inhibition of spinal motor neurons, and downregulation of inhibitory pathways.

Publication Types:

Review

PMID: 12715968 [PubMed - indexed for MEDLINE]

18: Can J Neurol Sci. 2000 Aug;27(3):220-8.

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Age-related changes in muscle fatigue resistance in humans.

Chan KM, Raja AJ, Strohschein FJ, Lechelt K.

Division of Physical Medicine and Rehabilitation, Faculty of Medicine, University of Alberta, Edmonton, Canada.

OBJECTIVE: The goal of this study was to compare the relative contributions from the muscle and the central nervous system to muscle fatigue resistance in aging. METHODS: Each subject carried out 90 s of sustained maximal voluntary isometric contraction (MVC) of the thumb using the thenar and forearm thumb muscles. Contractile capacity of the thenar muscles was assessed through tetanic stimulation of the median nerve. Interpolated doublets delivered during an MVC represented the overall voluntary activation level while transcranial cortical stimulation with an electromagnetic stimulator was used to assess motor output upstream from the corticomotoneuronal pathway. RESULTS: Nine elderly subjects [four females and five males, 70+/-9 years old (mean+/-SD)] and 10 younger subjects (five females and five males, 30+/-6 years old) were tested. After the fatiguing exercise, the elderly group's MVC declined by 29% as opposed to 47% in the younger group (p<0.01). The elderly group's greater fatigue resistance was accounted for by increased fatigue resistance at the muscle level as well as in the central nervous system. At least some of the decline in the central motor drive was upstream from the corticomotoneuronal pathway. CONCLUSION: The higher muscle fatigue resistance in the elderly group was attributable to differences in both the peripheral and central nervous systems.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 10975534 [PubMed - indexed for MEDLINE]

19: Neuropsychologia. 2004;42(7):944-56.

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From mental power to muscle power--gaining strength by using the mind.

Ranganathan VK, Siemionow V, Liu JZ, Sahgal V, Yue GH.

Department of Biomedical Engineering/ND20, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.

The purposes of this project were to determine mental training-induced strength gains (without performing physical exercises) in the little finger abductor as well as in the elbow flexor muscles, which are frequently used during daily living, and to quantify cortical signals that mediate maximal voluntary contractions (MVCs) of the two muscle groups. Thirty young, healthy volunteers participated in the study. The first group (N = 8) was trained to perform "mental contractions" of little finger abduction (ABD); the second group (N = 8) performed mental contractions of elbow (ELB) flexion; and the third group (N = 8) was not trained but participated in all measurements and served as a control group. Finally, six volunteers performed training of physical maximal finger abductions. Training lasted for 12 weeks (15 min per day, 5 days per week). At the end of training, we found that the ABD group had increased their finger abduction strength by 35% (P < 0.005) and the ELB group augmented their elbow flexion strength by 13.5% (P < 0.001). The physical training group increased the finger abduction strength by 53% (P < 0.01). The control group showed no significant changes in strength for either finger abduction or elbow flexion tasks. The improvement in muscle strength for trained groups was accompanied by significant increases in electroencephalogram-derived cortical potential, a measure previously shown to be directly related to control of voluntary muscle contractions. We conclude that the mental training employed by this study enhances the cortical output signal, which drives the muscles to a higher activation level and increases strength.

Publication Types:

PMID: 14998709 [PubMed - indexed for MEDLINE]

20: J Appl Physiol. 1998 Jan;84(1):284-91.

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Older adults can maximally activate the biceps brachii muscle by voluntary command.

De Serres SJ, Enoka RM.

Department of Biomedical Engineering, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.

Because some of the decline in strength with age may be explained by an impairment of muscle activation, the purpose of this study was to determine the activation level achieved in biceps brachii by older adults during a maximum voluntary contraction (MVC). This capability was assessed with two superimposition techniques: one calculated the activation level that was achieved during an MVC, and the other provided an estimate of the expected MVC force based on extrapolation with submaximal forces. The activation level in biceps brachii was incomplete (< 100%) for the young (n = 16) and elderly (n = 16) subjects, with the elderly subjects exhibiting the greater deficit. In contrast, there was no difference between the measured and expected MVC forces for either group of subjects, whether the extrapolation involved a third-order polynomial or linearization of the data. Because of the lower signal-to-noise ratio associated with the measurement of activation level and the greater number of measurements that contributed to the estimate of the expected MVC force, we conclude that the older adults were able to achieve complete activation of the biceps brachii muscle during an MVC.

Publication Types:

PMID: 9451648 [PubMed - indexed for MEDLINE]

21: J Appl Physiol. 2007 Jan;102(1):368-73. Epub 2006 Oct 19.

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Early skeletal muscle hypertrophy and architectural changes in response to high-intensity resistance training.

Seynnes OR, de Boer M, Narici MV.

Institute for Biophysical and Clinical Research Into Human Movement, Manchester Metropolitan University, Hassall Rd., Alsager ST7 2HL, UK. o.seynnes@mmu.ac.uk

The onset of whole muscle hypertrophy in response to overloading is poorly documented. The purpose of this study was to assess the early changes in muscle size and architecture during a 35-day high-intensity resistance training (RT) program. Seven young healthy volunteers performed bilateral leg extension three times per week on a gravity-independent flywheel ergometer. Cross-sectional area (CSA) in the central (C) and distal (D) regions of the quadriceps femoris (QF), muscle architecture, maximal voluntary contraction (MVC), and electromyographic (EMG) activity were measured before and after 10, 20, and 35 days of RT. By the end of the training period, MVC and EMG activity increased by 38.9 +/- 5.7 and 34.8% +/- 4.7%, respectively. Significant increase in QF CSA (3.5 and 5.2% in the C and D regions, respectively) was observed after 20 days of training, along with a 2.4 +/- 0.7% increase in fascicle length from the 10th day of training. By the end of the 35-day training period, the total increase in QF CSA for regions C and D was 6.5 +/- 1.1 and 7.4 +/- 0.8%, respectively, and fascicle length and pennation angle increased by 9.9 +/- 1.2 and 7.7 +/- 1.3%, respectively. The results show for the first time that changes in muscle size are detectable after only 3 wk of RT and that remodeling of muscle architecture precedes gains in muscle CSA. Muscle hypertrophy seems to contribute to strength gains earlier than previously reported; flywheel training seems particularly effective for inducing these early structural adaptations.

Publication Types:

Clinical Trial

PMID: 17053104 [PubMed - indexed for MEDLINE]

22: Med Sci Sports Exerc. 1988 Oct;20(5 Suppl):S135-45.

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Review

PMID: 3057313 [PubMed - indexed for MEDLINE]

23: J Appl Physiol. 2006 Dec;101(6):1766-75. Epub 2006 Jun 22.

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Training adaptations in the behavior of human motor units.

Duchateau J, Semmler JG, Enoka RM.

Laboratory of Applied Biology, Université Libre de Bruxelles, 28 Ave., P. Héger CP 168, 1000 Brussels, Belgium. jduchat@ulb.ac.be

The purpose of this brief review is to examine the neural adaptations associated with training, by focusing on the behavior of single motor units. The review synthesizes current understanding on motor unit recruitment and rate coding during voluntary contractions, briefly describes the techniques used to record motor unit activity, and then evaluates the adaptations that have been observed in motor unit activity during maximal and submaximal contractions. Relatively few studies have directly compared motor unit behavior before and after training. Although some studies suggest that the voluntary activation of muscle can increase slightly with strength training, it is not known how the discharge of motor units changes to produce this increase in activation. The evidence indicates that the increase is not attributable to changes in motor unit synchronization. It has been demonstrated, however, that training can increase both the rate of torque development and the discharge rate of motor units. Furthermore, both strength training and practice of a force-matching task can evoke adaptations in the discharge characteristics of motor units. Because the variability in discharge rate has a significant influence on the fluctuations in force during submaximal contractions, the changes produced with training can influence motor performance during activities of daily living. Little is known, however, about the relative contributions of the descending drive, afferent feedback, spinal circuitry, and motor neuron properties to the observed adaptations in motor unit activity.

Publication Types:

PMID: 16794023 [PubMed - indexed for MEDLINE]

24: Exerc Sport Sci Rev. 2000 Oct;28(4):177-84.

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Chronic neural adaptations to unilateral exercise: mechanisms of cross education.

Zhou S.

School of Exercise Science and Sport Management, Southern Cross University, Lismore, New South Wales, Australia. szhou@scu.edu.au

Cross education refers to the contralateral effect of chronic motor activity in one limb. The effect can enhance or diminish motor activity and is specific to the homologous muscles and the training task. The mechanisms underlying the phenomenon involve adaptations in the nervous system, probably at the level of the spinal cord.

Publication Types:

Comparative Study

PMID: 11064852 [PubMed - indexed for MEDLINE]

: Muscle maintenance by volitional contraction against applied electrical stimulation.

Nago T, Umezu Y, Shiba N, Matsuse H, Maeda T, Tagawa Y, Nagata K, Basford JR.

Rehabilitation Center, Kurume University, Kurume, Japan. nago_takeshi@kurume-u.ac.jp

Muscle training exercises are needed for muscular endurance during spaceflight. This study was designed to investigate effects of volitional contraction against applied electrical stimulation on the muscular endurance of the proximal upper extremity. Thirteen healthy sedentary men were allocated into two groups. One group participated in a hybrid (HYB) exercise regimen in which the biceps brachii was stimulated as he volitionally extended his elbow, and the triceps brachii was stimulated as the volitionally flexed his elbow. The second group underwent a similar regimen in which the electrical stimulation (ELS) was alternatively delivered to the biceps brachii and then to the triceps brachii with the limb fixed. Forty-second surface electromyography (EMG) recordings at 50% maximum voluntary contraction (MVC) were made as baseline data at just before starting the training regimen, and again conclusion. The median frequency (MF) and mean power frequency (MPF) slopes with time were determined using power spectrum analysis. There were statistical significance only for the triceps in which the MF and MPF slopes in the HYB Group became less negative over the period of study (from -45.7+/-14.7 and -47.0+/-8.6%/min at baseline to -36.9+/-10.7 and -36.8+/-7.0%/min at the end of training, respectively). The corresponding values for these slopes in the ELS Group showed opposite tends with less marked changes of borderline significance for MF and of statistical significance for MPF. These results suggested that the HYB exercise regimen was capable of producing an improvement in triceps but not biceps brachii.

PMID: 18332595 [PubMed - in process]

26: Can J Appl Physiol. 2005 Jun;30(3):341-51.

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Aging, resistance training, and motor unit discharge behavior.

Kamen G.

Dept. of Exercise Science, University of Massachusetts, Amherst, MA 01003, USA.

Researchers have alluded the existence of "neural factors" in the expression and development of muscular strength. Candidate neural factors including motor unit recruitment, rate coding, double firing, and motor unit synchronization are discussed in this review. Aging is generally accompanied by lower motor unit discharge rates. However, both young and older adults exhibit rapid changes in muscular strength with repeated strength testing. These strength changes occur with concomitant albeit transient increase in motor unit discharge rate. These and other neural factors may contribute to the initial increase in muscular strength observed during the early phases of resistance exercise training.

Publication Types:

Review

PMID: 16129898 [PubMed - indexed for MEDLINE]

1: J Strength Cond Res. 2007 Aug;21(3):768-75.

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Detraining and tapering effects on hormonal responses and strength performance.

Izquierdo M, Ibañez J, González-Badillo JJ, Ratamess NA, Kraemer WJ, Häkkinen K, Bonnabau H, Granados C, French DN, Gorostiaga EM.

Studies, Research and Sport Medicine Center, Government of Navarra, Navarra, Spain. mikel.izquierdo@ceimd.org

This study examined the impact of 4 weeks of either complete cessation of training (DTR) or a tapering period (TAP; short-term reduction of the strength training volume, while the intensity is kept high), subsequent to 16 weeks of periodized heavy resistance training (PRT) on strength/power gains and the underlying physiologic changes in basal circulating anabolic/catabolic hormones in strength-trained athletes. Forty-six physically active men were matched and randomly assigned to a TAP (n = 11), DTR (n = 14), or control group (C; n = 21), subsequent to a 16-week PRT program. Muscular and power testing and blood draws to determine basal hormonal concentrations were conducted before the initiation of training (T0), after 16 weeks of training (T1), and after 4 weeks of either DTR or TAP (T2). Short-term DTR (4 weeks) results in significant decreases in maximal strength (-6 to -9%) and muscle power output (-17 and -14%) of the arm and leg extensor muscles. However, DTR had a significant (p < 0.01) larger effect on muscle power output more than on strength measurements of both upper and lower extremity muscles. Short-term (4 weeks) TAP reached further increases for leg (2%) and arm (2%) maximal strength, whereas no further changes were observed in both upper and lower muscle power output. Short-term DTR resulted in a tendency for elevation resting serum insulin-like growth factor (IGF)-1 concentrations, whereas the corresponding TAP experienced elevation in resting serum insulin-like binding protein-3 (IGFBP-3). These data indicated that DTR may induce larger declines in muscle power output than in maximal strength, whereas TAP may result in further strength enhancement (but not muscle power), mediated, in part, by training-related differences in IGF-1 and IGFBP-3 concentrations.

Publication Types:

PMID: 17685721 [PubMed - indexed for MEDLINE]

2: J Strength Cond Res. 2007 Feb;21(1):157-63.

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Dissimilar effects of one- and three-set strength training on strength and muscle mass gains in upper and lower body in untrained subjects.

Rønnestad BR, Egeland W, Kvamme NH, Refsnes PE, Kadi F, Raastad T.

Norwegian College of Sport Sciences, Oslo.

The purpose of this study was to compare the effects of single- and multiple-set strength training on hypertrophy and strength gains in untrained men. Twenty-one young men were randomly assigned to either the 3L-1UB group (trained 3 sets in leg exercises and 1 set in upper-body exercises; n = 11), or the 1L-3UB (trained 1 set in leg exercises and 3 sets in upper-body exercises; n = 10). Subjects trained 3 days per week for 11 weeks and each workout consisted of 3 leg exercises and 5 upper-body exercises. Training intensity varied between 10 repetition maximum (RM) and 7RM. Strength (1RM) was tested in all leg and upper-body exercises and in 2 isokinetic tests before training, and after 3, 6, 9, and 11 weeks of training. Cross sectional area (CSA) of thigh muscles and the trapezius muscle and body composition measures were performed before training, and after 5 and 11 weeks of training. The increase in 1RM from week 0 to 11 in the lower-body exercises was significantly higher in the 3L-1UB group than in the 1L-3UB group (41 vs. 21%; p < 0.001), while no difference existed between groups in upper-body exercises. Peak torque in maximal isokinetic knee-extension and thigh CSA increased more in the 3L-1UB group than in the 1L-3UB group (16 vs. 8%; p = 0.03 and 11 vs. 7%; p = 0.01, respectively), while there was no significant difference between groups in upper trapezius muscle CSA. The results demonstrate that 3-set strength training is superior to 1-set strength training with regard to strength and muscle mass gains in the leg muscles, while no difference exists between 1- and 3-set training in upper-body muscles in untrained men.

Publication Types:

PMID: 17313291 [PubMed - indexed for MEDLINE]

3: Br J Sports Med. 2007 Jan;41(1):19-22. Epub 2006 Oct 24.

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Comparison of once-weekly and twice-weekly strength training in older adults.

DiFrancisco-Donoghue J, Werner W, Douris PC.

Academic Health Care Center of The New York College of Osteopathic Medicine, Old Westbury, New York, USA.

BACKGROUND: Strength training has been shown to benefit the health and function of older adults. OBJECTIVE: To investigate whether one set of exercises performed once a week was as effective in increasing muscle strength as training twice a week. METHODS: 18 subjects (7 women and 11 men) aged 65-79 years were randomly assigned to two groups. Both groups performed one set of exercises to muscular fatigue; group 1 trained 1 day/week and group 2 trained 2 days/week on three lower and three upper body exercises for 9 weeks. The data were analysed using a mixed model 2 x 2 analysis of variance. RESULTS: A significant main effect of time (p<0.001), but not group, on one-repetition maximum scores was observed. No significant interaction was observed between time and group and therefore no difference in strength changes between training once a week versus twice a week after 9 weeks. CONCLUSIONS: One set of exercises performed once weekly to muscle fatigue improved strength as well as twice a week in the older adult. Our results provide information that will assist in designing strength-training programmes that are more time and cost efficient in producing health and fitness benefits for older adults.

Publication Types:

PMID: 17062657 [PubMed - indexed for MEDLINE]

4: J Appl Physiol. 2007 Jan;102(1):368-73. Epub 2006 Oct 19.

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Clinical Trial

PMID: 17053104 [PubMed - indexed for MEDLINE]

5: Exp Brain Res. 2006 Nov;175(4):745-53. Epub 2006 Oct 19.

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Motor unit synchronization measured by cross-correlation is not influenced by short-term strength training of a hand muscle.

Kidgell DJ, Sale MV, Semmler JG.

School of Exercise and Nutrition Sciences, Deakin University, Burwood, VIC, Australia.

The purpose of the study was to quantify the strength of motor unit synchronization and coherence from pairs of concurrently active motor units before and after short-term (4-8 weeks) strength training of the left first dorsal interosseous (FDI) muscle. Five subjects (age 24.8 +/- 4.3 years) performed a training protocol three times/week that consisted of six sets of ten maximal isometric index finger abductions, whereas three subjects (age 27.3 +/- 6.7 years) acted as controls. Motor unit activity was recorded from pairs of intramuscular electrodes in the FDI muscle with two separate motor unit recording sessions obtained before and after strength training (trained group) or after 4 weeks of normal daily activities that did not involve training (control group). The training intervention resulted in a 54% (45.2 +/- 8.3 to 69.5 +/- 13.8 N, P = 0.001) increase in maximal index finger abduction force, whereas there was no change in strength in the control group. A total of 163 motor unit pairs (198 single motor units) were examined in both subject groups, with 52 motor unit pairs obtained from 10 recording sessions before training and 51 motor unit pairs from 10 recording sessions after training. Using the cross-correlation procedure, there was no change in the strength of motor unit synchronization following strength training (common input strength index; 0.71 +/- 0.41 to 0.67 +/- 0.43 pulses/s). Furthermore, motor unit coherence z scores at low (0-10 Hz; 3.9 +/- 0.3 before to 4.4 +/- 0.4 after) or high (10-30 Hz; 1.7 +/- 0.1 before to 1.9 +/- 0.1 after) frequencies were not influenced by strength training. These motor unit data indicate that increases in strength following several weeks of training a hand muscle are not accompanied by changes in motor unit synchronization or coherence, suggesting that these features of correlated motor unit activity are not important in the expression of muscle strength.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 17051382 [PubMed - indexed for MEDLINE]

6: Med Sci Sports Exerc. 2006 Oct;38(10):1770-81.

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Muscular performance after concentric and eccentric exercise in trained men.

Vikne H, Refsnes PE, Ekmark M, Medbø JI, Gundersen V, Gundersen K.

Norwegian School of Sport Sciences, Oslo, Norway.

PURPOSE: We studied previously resistance-trained men and compared the effects of concentric and eccentric training on performance and structural muscle parameters. METHODS: Seventeen trained individuals (age 26.9 +/- 3.4 yr) participated in 12 wk of either maximum concentric (N = 8) or eccentric (N = 9) resistance training of the elbow flexors. The functional performance was measured as the maximum concentric and eccentric strength and angular velocity at standard loads. Muscle cross-sectional area and cross-sectional area of single cells were used as measures of muscular hypertrophy. Fiber-type proportions were assessed by staining cells for myofibrillar ATPase. RESULTS: Both eccentric and concentric training increased concentric strength to a similar extent (14 vs 18%), whereas eccentric training led to greater increases in eccentric strength than concentric training did (26 vs 9%). The maximum angular velocity at all loads was enhanced equally in both training groups. The cross-sectional area of both the elbow flexors (+11%) and of the type I and type IIA fibers increased only after the eccentric training. In addition, the relative cross-sectional area occupied by the type II fibers increased from 64 to 73% after the eccentric training. There were only minor changes in the fiber-type proportions. CONCLUSION: The present data suggest that for resistance-trained men, increases in concentric strength and velocity performance after eccentric training are largely mediated by changes in fiber and muscle cross-sectional area. However, hypertrophy alone could not explain the increase in eccentric strength. Because the increases in strength and velocity performance after concentric training could not be ascribed to muscular adaptations alone, we suggest that they may be attributable to additional neural factors.

Publication Types:

PMID: 17019299 [PubMed - indexed for MEDLINE]

7: J Neurosci. 2006 May 3;26(18):4796-802.

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PMID: 16672652 [PubMed - indexed for MEDLINE]

8: J Appl Physiol. 2006 May;100(5):1647-56. Epub 2006 Jan 12.

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Differential effects of strength training leading to failure versus not to failure on hormonal responses, strength, and muscle power gains.

Izquierdo M, Ibañez J, González-Badillo JJ, Häkkinen K, Ratamess NA, Kraemer WJ, French DN, Eslava J, Altadill A, Asiain X, Gorostiaga EM.

Studies, Research and Sport Medicine Center, Government of Navarra, Spain. mikel.izquierdo@ceimd.org

The purpose of this study was to examine the efficacy of 11 wk of resistance training to failure vs. nonfailure, followed by an identical 5-wk peaking period of maximal strength and power training for both groups as well as to examine the underlying physiological changes in basal circulating anabolic and catabolic hormones. Forty-two physically active men were matched and then randomly assigned to either a training to failure (RF; n = 14), nonfailure (NRF; n = 15), or control groups (C; n = 13). Muscular and power testing and blood draws to determine basal hormonal concentrations were conducted before the initiation of training (T0), after 6 wk of training (T1), after 11 wk of training (T2), and after 16 wk of training (T3). Both RF and NRF resulted in similar gains in 1-repetition maximum bench press (23 and 23%) and parallel squat (22 and 23%), muscle power output of the arm (27 and 28%) and leg extensor muscles (26 and 29%), and maximal number of repetitions performed during parallel squat (66 and 69%). RF group experienced larger gains in the maximal number of repetitions performed during the bench press. The peaking phase (T2 to T3) after NRF resulted in larger gains in muscle power output of the lower extremities, whereas after RF it resulted in larger gains in the maximal number of repetitions performed during the bench press. Strength training leading to RF resulted in reductions in resting concentrations of IGF-1 and elevations in IGFBP-3, whereas NRF resulted in reduced resting cortisol concentrations and an elevation in resting serum total testosterone concentration. This investigation demonstrated a potential beneficial stimulus of NRF for improving strength and power, especially during the subsequent peaking training period, whereas performing sets to failure resulted in greater gains in local muscular endurance. Elevation in IGFBP-3 after resistance training may have been compensatory to accommodate the reduction in IGF-1 to preserve IGF availability.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 16410373 [PubMed - indexed for MEDLINE]

9: Eur J Appl Physiol. 2006 Apr;96(6):722-8. Epub 2006 Feb 28.

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Research Support, Non-U.S. Gov't

PMID: 16506058 [PubMed - indexed for MEDLINE]

10: Yonsei Med J. 2006 Feb 28;47(1):93-104.

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Quantitative EMG changes during 12-week DeLorme's axiom strength training.

Shin HK, Cho SH, Lee YH, Kwon OY.

Department of Occupational Therapy, Kaya University, College of Health Science, Goryeong-gun, Gyeongbuk 717-800, Korea. hkshin1@kaya.ac.kr

Strength training is one of the most common exercises practiced in the field of physical therapy or sports training. However, limited methodology is available to evaluate its effect on the target muscle. This study aimed to test the hypothesis that surface electromyographic (EMG) data from both isometric and isotonic exercise can express changes within the muscle during a 12-week strength training program. Ten healthy male volunteer students (5 for training, 5 for controls) from Yonsei University were recruited for evaluation in this study. DeLorme's axiom was practiced for 12 weeks in the dominant elbow flexors and knee extensors of the training group. Tension for 1 repetition maximum and maximal voluntary isometric contraction, and surface EMG information such as the integrated EMG and three variables from the regression line of median frequency (MDF) data were measured at weeks 0, 3, 6, 9, and 12. The limb circumference was measured at weeks 0 and 12. During the strength training, which was enough for the increment of muscle strength and limb circumference, the rectified-integrated EMG and initial MDF increased with a significant linear pattern in both types of contraction. The two surface EMG variables were able to monitor the physiologic muscle changes during the training. Based on these results, we propose that these two surface EMG variables can be used for monitoring electrophysiological changes in the specific muscle that is undergoing the training program, under conditions where the contraction mode for EMG data collection is either static or dynamic.

Publication Types:

PMID: 16502490 [PubMed - indexed for MEDLINE]

11: Sports Med. 2006;36(2):133-49.

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PMID: 16464122 [PubMed - indexed for MEDLINE]

12: J Appl Physiol. 2005 Nov;99(5):1880-4. Epub 2005 Jul 14.

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Training with unilateral resistance exercise increases contralateral strength.

Munn J, Herbert RD, Hancock MJ, Gandevia SC.

School of Physiotherapy, The University of Sydney, PO Box 170, Lidcombe NSW, 1825 Australia. J.Munn@fhs.usyd.edu.au

Evidence that unilateral training increases contralateral strength is inconsistent, possibly because existing studies have design limitations such as lack of control groups, lack of randomization, and insufficient statistical power. This study sought to determine whether unilateral resistance training increases contralateral strength. Subjects (n = 115) were randomly assigned to a control group or one of the following four training groups that performed supervised elbow flexion contractions: 1) one set at high speed, 2) one set at low speed, 3) three sets at high speed, or 4) three sets at low speed. Training was 3 times/wk for 6 wk with a six- to eight-repetition maximum load. Control subjects attended sessions but did not exercise. Elbow flexor strength was measured with a one-repetition maximum arm curl before and after training. Training with one set at slow speed did not produce an increase in contralateral strength (mean effect of -1% or -0.07 kg; 95% confidence interval: -0.42-0.28 kg; P = 0.68). However, three sets increased strength of the untrained arm by a mean of 7% of initial strength (additional mean effect of 0.41 kg; 95% confidence interval: 0.06-0.75 kg; P = 0.022). There was a tendency for training with fast contractions to produce a greater increase in contralateral strength than slow training (additional mean effect of 5% or 0.31 kg; 95% confidence interval: -0.03-0.66 kg; P = 0.08), but there was no interaction between the number of sets and training speed. We conclude that three sets of unilateral resistance exercise produce small contralateral increases in strength.

Publication Types:

Randomized Controlled Trial

PMID: 16024518 [PubMed - indexed for MEDLINE]

13: J Appl Physiol. 2005 Oct;99(4):1558-68. Epub 2005 May 12.

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Research Support, Non-U.S. Gov't

PMID: 15890749 [PubMed - indexed for MEDLINE]

14: Phys Ther. 2005 Oct;85(10):1053-60.

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Can mental practice increase ankle dorsiflexor torque?

Sidaway B, Trzaska AR.

Department of Physical Therapy, Husson College, One College Circle, Bangor, ME 04401, USA. sidawayb@husson.edu

BACKGROUND AND PURPOSE: Mental practice has been shown to be effective in increasing the force production of the abductor digiti minimi muscle in the hand. The aim of this study was to determine whether mental practice could produce strength gains in the larger ankle dorsiflexor muscles, which are important during walking. SUBJECTS: Twenty-four subjects were randomly assigned to a physical practice group, a mental practice group, or a control group (8 subjects per group). METHODS: In the practice groups, subjects either physically or mentally practiced producing maximal isometric contractions for 3 sets of 10 repetitions, 3 times per week for 4 weeks. Changes in mean peak isometric torque normalized to body weight and the resulting percentage of improvement were analyzed across the 3 groups. RESULTS: Differences in raw torque production after training in the 2 practice groups resulted in significant percentages of improvement for the physical practice group (25.28%) and the mental practice group (17.13%), but not for the control group (-1.77%). The 2 practice groups were not statistically different in their maximal torque-generating capacity after training. DISCUSSION AND CONCLUSION: These findings show that mental practice in people without impairments can lead to an increase in torque production similar to that produced by physical practice. Such a technique may prove to be a useful adjunct to traditional treatment options aimed at increasing muscle strength.

Publication Types:

PMID: 16180954 [PubMed - indexed for MEDLINE]

15: J Physiol. 2005 Aug 15;567(Pt 1):337-48. Epub 2005 Jun 9.

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Maximal force, voluntary activation and muscle soreness after eccentric damage to human elbow flexor muscles.

Prasartwuth O, Taylor JL, Gandevia SC.

Prince of Wales Medical Research Institute, University of New South Wales, Barker Street, Randwick, Sydney, NSW 2031, Australia.

Muscle damage reduces voluntary force after eccentric exercise but impaired neural drive to the muscle may also contribute. To determine whether the delayed-onset muscle soreness, which develops approximately 1 day after exercise, reduces voluntary activation and to identify the possible site for any reduction, voluntary activation of elbow flexor muscles was examined with both motor cortex and motor nerve stimulation. We measured maximal voluntary isometric torque (MVC), twitch torque, muscle soreness and voluntary activation in eight subjects before, immediately after, 2 h after, 1, 2, 4 and 8 days after eccentric exercise. Motor nerve stimulation and motor cortex stimulation were used to derive twitch torques and measures of voluntary activation. Eccentric exercise immediately reduced the MVC by 38 +/- 3% (mean +/- s.d., n = 8). The resting twitch produced by motor nerve stimulation fell by 82 +/- 6%, and the estimated resting twitch by cortical stimulation fell by 47 +/- 15%. While voluntary torque recovered after 8 days, both measures of the resting twitch remained depressed. Muscle tenderness occurred 1-2 days after exercise, and pain during contractions on days 1-4, but changes in voluntary activation did not follow this time course. Voluntary activation assessed with nerve stimulation fell 19 +/- 6% immediately after exercise but was not different from control values after 2 days. Voluntary activation assessed by motor cortex stimulation was unchanged by eccentric exercise. During MVCs, absolute increments in torque evoked by nerve and cortical stimulation behaved differently. Those to cortical stimulation decreased whereas those to nerve stimulation tended to increase. These findings suggest that reduced voluntary activation contributes to the early force loss after eccentric exercise, but that it is not due to muscle soreness. The impairment of voluntary activation to nerve stimulation but not motor cortical stimulation suggests that the activation deficit lies in the motor cortex or at a spinal level.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 15946963 [PubMed - indexed for MEDLINE]

PMCID: PMC1474152

16: J Strength Cond Res. 2005 Aug;19(3):689-97.

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Moderate resistance training volume produces more favorable strength gains than high or low volumes during a short-term training cycle.

González-Badillo JJ, Gorostiaga EM, Arellano R, Izquierdo M.

Spanish Olympic Committee, Madrid, Spain. jjgbadi@arrakis.es

The purpose of this study was to examine the effects of 3 resistance training volumes on maximal strength in the snatch (Sn), clean & jerk (C&J), and squat (Sq) exercises during a 10-week training period. Fifty-one experienced (>3 years), trained junior lifters were randomly assigned to one of 3 groups: a low-volume group (LVG, n = 16), a moderate-volume group (MVG, n = 17), and a high-volume group (HVG, n = 18). All subjects trained 4-5 days a week with a periodized routine using the same exercises and relative intensities but a different total number of sets and repetitions at each relative load: LVG (1,923 repetitions), MVG (2,481 repetitions), and HVG (3,030 repetitions). The training was periodized from moderate intensity (60- 80% of 1 repetition maximum [1RM]) and high number of repetitions per set (2-6) to high intensity (90-100% of 1RM) and low number of repetitions per set (1-3). During the training period, the MVG showed a significant increase for the Sn, C&J, and Sq exercises (6.1, 3.7, and 4.2%, respectively, p < 0.01), whereas in the LVG and HVG, the increase took place only with the C&J exercise (3.7 and 3%, respectively, p < 0.05) and the Sq exercise (4.6%, p < 0.05, and 4.8%, p < 0.01, respectively). The increase in the Sn exercise for the MVG was significantly higher than in the LVG (p = 0.015). Calculation of effect sizes showed higher strength gains in the MVG than in the HVG or LVG. There were no significant differences between the LVG and HVG training volume-induced strength gains. The present results indicate that junior experienced lifters can optimize performance by exercising with only 85% or less of the maximal volume that they can tolerate. These observations may have important practical relevance for the optimal design of strength training programs for resistance-trained athletes, since we have shown that performing at a moderate volume is more effective and efficient than performing at a higher volume.

Publication Types:

PMID: 16095427 [PubMed - indexed for MEDLINE]

17: J Appl Physiol. 2005 Jul;99(1):87-94. Epub 2005 Feb 24.

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Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining.

Andersen LL, Andersen JL, Magnusson SP, Suetta C, Madsen JL, Christensen LR, Aagaard P.

Institute of Sports Medicine Copenhagen/Team Danmark Testcenter, Bispebjerg Hospital, Build. 8, 2nd floor, DK-2400 Copenhagen. ll_andersen@yahoo.dk

Previous studies show that cessation of resistance training, commonly known as "detraining," is associated with strength loss, decreased neural drive, and muscular atrophy. Detraining may also increase the expression of fast muscle myosin heavy chain (MHC) isoforms. The present study examined the effect of detraining subsequent to resistance training on contractile performance during slow-to-medium velocity isokinetic muscle contraction vs. performance of maximal velocity "unloaded" limb movement (i.e., no external loading of the limb). Maximal knee extensor strength was measured in an isokinetic dynamometer at 30 and 240 degrees/s, and performance of maximal velocity limb movement was measured with a goniometer during maximal unloaded knee extension. Muscle cross-sectional area was determined with MRI. Electromyographic signals were measured in the quadriceps and hamstring muscles. Twitch contractions were evoked in the passive vastus lateralis muscle. MHC isoform composition was determined with SDS-PAGE. Isokinetic muscle strength increased 18% (P < 0.01) and 10% (P < 0.05) at slow and medium velocities, respectively, along with gains in muscle cross-sectional area and increased electromyogram in response to 3 mo of resistance training. After 3 mo of detraining these gains were lost, whereas in contrast maximal unloaded knee extension velocity and power increased 14% (P < 0.05) and 44% (P < 0.05), respectively. Additionally, faster muscle twitch contractile properties along with an increased and decreased amount of MHC type II and MHC type I isoforms, respectively, were observed. In conclusion, detraining subsequent to resistance training increases maximal unloaded movement speed and power in previously untrained subjects. A phenotypic shift toward faster muscle MHC isoforms (I --> IIA --> IIX) and faster electrically evoked muscle contractile properties in response to detraining may explain the present results.

Publication Types:

PMID: 15731398 [PubMed - indexed for MEDLINE]

18: J Sci Med Sport. 2005 Jun;8(2):190-9.

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A comparison of periodised and fixed repetition training protocol on strength in older adults.

DeBeliso M, Harris C, Spitzer-Gibson T, Adams KJ.

Department of Kinesiology, Boise State University, Boise, Idaho, USA.

It has been forwarded that strength training is the primary intervention for improving and maintaining functional independence of the elderly. The purpose of this study was to determine if a periodised strength-training program was superior to a fixed repetition protocol for enhancing strength in older adults. Previously untrained male and female participants (71.6+/-5.3 y) were separated into three groups: fixed repetition (FR: n= 18), periodised (PER: n= 21) and control (C: n= 21). FR and PER protocols trained 2 days/week performing knee extensions, leg press, leg curl, biceps curl, triceps extension, lat pull downs, shoulder press and seated bench press. FR performed three sets of 9RM/exercise throughout the 18-week study. PER performed two sets of 15RM/exercise (weeks 1-6), three sets of 9RM/exercise (weeks 7-12) and four sets of 6RM/exercise (weeks 13-18). Pre-post 1RM were collected for each exercise. The sum of 1RM for the eight exercises was considered indicative of total body strength and served as the dependent variable. An ANOVA with Bonferroni post hoc was utilised to analyse the data. FR (p< 0.01) and PER (p< 0.01) groups experienced significant strength gains compared to C but were not different from each other. The results suggest that previously untrained older adults could expect similar strength gains from FR or PER strength-training protocols of 18 weeks or less.

Publication Types:

PMID: 16075779 [PubMed - indexed for MEDLINE]

19: J Appl Physiol. 2005 May;98(5):1768-76. Epub 2005 Jan 7.

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Short-term high- vs. low-velocity isokinetic lengthening training results in greater hypertrophy of the elbow flexors in young men.

Shepstone TN, Tang JE, Dallaire S, Schuenke MD, Staron RS, Phillips SM.

Exercise of Metabolism Research Group, Department of Kinesiology, McMaster University, 1280 Main St. W., Hamilton, ON, Canada L8S 4K1.

We performed two studies to determine the effect of a resistive training program comprised of fast vs. slow isokinetic lengthening contractions on muscle fiber hypertrophy. In study I, we investigated the effect of fast (3.66 rad/s; Fast) or slow (0.35 rad/s; Slow) isokinetic high-resistance muscle lengthening contractions on muscle fiber and whole muscle cross-sectional area (CSA) of the elbow flexors was investigated in young men. Twelve subjects (23.8 +/- 2.4 yr; means +/- SD) performed maximal resistive lengthening isokinetic exercise with both arms for 8 wk (3 days/wk), during which they trained one arm at a Fast velocity while the contralateral arm performed an equivalent number of contractions at a Slow velocity. Before (Pre) and after (Post) the training, percutaneous muscle biopsies were taken from the midbelly of the biceps brachii and analyzed for fiber type and CSA. Type I muscle fiber size increased Pre to Post (P < 0.05) in both Fast and Slow arms. Type IIa and IIx muscle fiber CSA increased in both arms, but the increases were greater in the Fast- vs. the Slow-trained arm (P < 0.05). Elbow flexor CSA increased in Fast and Slow arms, with the increase in the Fast arm showing a trend toward being greater (P = 0.06). Maximum torque-generating capacity also increased to a greater degree (P < 0.05) in the Fast arm, regardless of testing velocity. In study II, we attempted to provide some explanation of the greater hypertrophy observed in study I by examining an indicator of protein remodeling (Z-line streaming), which we hypothesized would be greater in the Fast condition. Nine men (21.7 +/- 2.4 yr) performed an acute bout (n = 30, 3 sets x 10 repetitions/set) of maximal lengthening contractions at Fast and Slow velocities used in the training study. Biopsies revealed that Fast lengthening contractions resulted in more (185 +/- 1 7%; P < 0.01) Z-band streaming per millimeter squared muscle vs. the Slow arm. In conclusion, training using Fast (3.66 rad/s) lengthening contractions leads to greater hypertrophy and strength gains than Slow (0.35 rad/s) lengthening contractions. The greater hypertrophy seen in the Fast-trained arm (study I) may be related to a greater amount of protein remodeling (Z-band streaming; study II).

Publication Types:

PMID: 15640387 [PubMed - indexed for MEDLINE]

20: J Strength Cond Res. 2004 Nov;18(4):765-70.

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Strength/power augmentation subsequent to short-term training abstinence.

Weiss LW, Wood LE, Fry AC, Kreider RB, Relyea GE, Bullen DB, Grindstaff PD.

Musculoskeletal Dynamics Laboratory, Department of Health and Sport Sciences, University of Memphis, Memphis, TN 38152-3480. lweiss@memphis.edu

Strength augmentation has been demonstrated in resistance-trained men subsequent to 4 days of training abstinence. However, this phenomenon was exhibited in an unusual circumstance in which the exercise test (seated heel raise) primarily involved an isolated skeletal muscle (soleus) that is normally comprised almost exclusively of 1 fiber type. It is unclear if similar results would be found for aggregate muscle actions. Therefore, a comparable study was designed with this in mind. Subjects were apparently healthy, young, strength-trained men (n = 25). All performed various tests of bench press strength at the beginning of their last standardized dynamic constant external resistance (DCER) training session. Subjects were subsequently randomly assigned to 1 of 4 groups and repeated the identical tests at intervals of either 2, 3, 4, or 5 days with no intervening training. Strength tests consisted of 1 repetition maximum (1RM) concentric-only isokinetic bench presses performed at 1.49 and 0.37 m.s(-1) as well as a 1RM DCER bench press. Measures of peak force and power were obtained from the isokinetic tests and maximum load from the DCER test. Results were expressed in both absolute and relative (to body weight) terms. Subsequent to the 4 abstinence intervals, groups performed similarly (p > 0.05) for all dependent variables. Concurrently, however, a small effect size (ES) was found for the group having a 4-day respite for both absolute and relative expressions of peak force and power at the slowest isokinetic bench press velocity. A small ES was also identified for the group having 2 days of rest for relative peak force at the slowest isokinetic test velocity and for relative DCER strength. Therefore, modest and transient strength augmentation appears likely in aggregate muscle actions following 2-4 days of training abstinence in resistance-trained men, but only at relatively slow velocities.

Publication Types:

PMID: 15574080 [PubMed - indexed for MEDLINE]

21: Brain Res. 2004 Oct 15;1023(2):200-12.

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Distinct brain activation patterns for human maximal voluntary eccentric and concentric muscle actions.

Fang Y, Siemionow V, Sahgal V, Xiong F, Yue GH.

Department of Biomedical Engineering/ND20, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.

Eccentric muscle contractions generate greater force at a lower level of activation and subject muscles to more severe damage than do concentric actions. A recent investigation has revealed that electroencephalogram (EEG)-derived movement-related cortical potential (MRCP) is greater and occurs earlier for controlling human eccentric than concentric submaximal muscle contractions. However, whether the central nervous system (CNS) control signals for high-intensity or maximal-effort eccentric movements differ from those for concentric actions is unknown. The purpose of this study was to determine whether the MRCP signals differ between the two types of maximal-effort contractions. Eight volunteers performed 40 maximal voluntary eccentric and 40 maximal voluntary concentric elbow flexor contractions on a Kin-Com isokinetic dynamometer. Scalp EEG signals (62 channels) were measured along with force, joint angle, and electromyographic (EMG) signals of the performing muscles. MRCP-based two-dimensional brain maps were created to illustrate spatial and temporal distributions of the MRCP signals. Although the level of elbow flexor muscle activity was lower during eccentric than concentric movements, MRCP-indicated cortical activation was greater both in amplitude and area dimension for the eccentric task. Detailed comparisons of individual electrode signals suggested that eccentric movements needed a significantly longer time for early preparation and a significantly greater magnitude of cortical activity for later movement execution. The extra preparation time and higher amplitude of activation may reflect CNS activities that account for the higher risk of injury, higher degree of movement difficulty, and unique motor unit activation pattern associated with maximal-level eccentric muscle actions.

Publication Types:

PMID: 15374746 [PubMed - indexed for MEDLINE]

22: Int J Neurosci. 2004 Jun;114(6):671-92.

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Cumulative effects of intermittent maximal contractions on voluntary activation deficits.

Simpson M, Burke JR, Davis JM.

Department of Exercise Science, School of Public Health, University of South Carolina, Columbia, 29208, USA.

The purpose of this research was to provide more definitive support for the hypothesis that prolonged muscle activation at high intensities increases voluntary activation deficits. Interpolated twitch responses were evoked during maximal and sub-maximal voluntary contractions of the soleus muscle in 10 college-aged students. Maximal voluntary contractions (MVC), maximal muscle twitches, and interpolated twitch responses were measured before, during, and after fatiguing isometric exercise, five bouts of 20 intermittent MVCs. The relationship between voluntary activation and force was studied by evoking interpolated twitches during sub-maximal voluntary contractions on Day 1 and pre-post fatigue on Day 2. Intraclass reliability coefficients for the MVC, maximal muscle twitch, and interpolated twitch responses were adequate across trials and days (R > or = .80). MVC force and maximal twitch force decreased after the fatiguing exercise bouts by 28% and 32%, respectively (p < .05). Voluntary activation of the fatigue-resistant soleus muscle decreased by 10% after the first five min of maximal exercise with a subsequent decrease of 9% occurring after 25 min of maximal exercise (p < .05). At the end of the experimental session, approximately 30 min after the end of the fatiguing exercise, decreases in 100% MVC force, maximal muscle twitch force, and voluntary activation were still evident: 22%, 23%, and 11%, respectively (p < .05). Post-fatigue, there were also changes in neural strategies for voluntary activation of the soleus muscle at the higher sub-maximal efforts, > or = 70% MVC target levels (p < .05). These data demonstrate the cumulative effects of prolonged exercise on voluntary activation.

Publication Types:

Comparative Study

PMID: 15204059 [PubMed - indexed for MEDLINE]

23: J Strength Cond Res. 2004 May;18(2):377-82.

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Maximizing strength development in athletes: a meta-analysis to determine the dose-response relationship.

Peterson MD, Rhea MR, Alvar BA.

Department of Exercise and Wellness, Arizona State University, Mesa, Arizona 85212, USA. mdpeterz@hotmail.com

The efficiency, safety, and effectiveness of strength training programs are paramount for sport conditioning. Therefore, identifying optimal doses of the training variables allows for maximal gains in muscular strength to be elicited per unit of time and also for the reduction in risk of overtraining and/or overuse injuries. A quantified dose-response relationship for the continuum of training intensities, frequencies, and volumes has been identified for recreationally trained populations but has yet to be identified for competitive athletes. The purpose of this analysis was to identify this relationship in collegiate, professional, and elite athletes. A meta-analysis of 37 studies with a total of 370 effect sizes was performed to identify the dose-response relationship among competitive athletes. Criteria for study inclusion were (a) participants must have been competitive athletes at the collegiate or professional level, (b) the study must have employed a strength training intervention, and (c) the study must have included necessary data to calculate effect sizes. Effect size data demonstrate that maximal strength gains are elicited among athletes who train at a mean training intensity of 85% of 1 repetition maximum (1RM), 2 days per week, and with a mean training volume of 8 sets per muscle group. The current data exhibit different dose-response trends than previous meta-analytical investigations with trained and untrained nonathletes. These results demonstrate explicit dose-response trends for maximal strength gains in athletes and may be directly used in strength and conditioning venues to optimize training efficiency and effectiveness.

Publication Types:

Meta-Analysis

PMID: 15142003 [PubMed - indexed for MEDLINE]

24: Neuropsychologia. 2004;42(7):944-56.

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PMID: 14998709 [PubMed - indexed for MEDLINE]

25: J Appl Physiol. 2003 Oct;95(4):1485-92. Epub 2003 Jun 27.

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Strength training counteracts motor performance losses during bed rest.

Shinohara M, Yoshitake Y, Kouzaki M, Fukuoka H, Fukunaga T.

Dept. of Integrative Physiology, Univ. of Colorado, Boulder, CO 80309-0354, USA. shinohara@colorado.edu

The purpose of the study was to determine the effect of bed rest with or without strength training on torque fluctuations and activation strategy of the muscles. Twelve young men participated in a 20-day bed rest study. Subjects were divided into a non-training group (BRCon) and a strength-training group (BRTr). The training comprised dynamic calf-raise and leg-press exercises. Before and after bed rest, subjects performed maximal contractions and steady submaximal isometric contractions of the ankle extensor muscles and of the knee extensor muscles (2.5-10% of maximal torque). Maximal torque decreased for both the ankle extensors (9%, P < 0.05) and knee extensors (16%, P < 0.05) in BRCon but not in BRTr. For the ankle extensors, the coefficient of variation (CV) for torque increased in both groups (P < 0.05), with a greater amount (P < 0.05) in BRCon (88%) compared with BRTr (41%). For the knee extensors, an increase in the CV for torque was observed only in BRCon (22%). The increase in the CV for torque in BRCon accompanied the greater changes in electromyogram amplitude of medial gastrocnemius (122%) and vastus lateralis (59%) compared with BRTr (P < 0.05). The results indicate that fluctuations in torque during submaximal contractions of the extensor muscles in the leg increase after bed rest and that strength training counteracted the decline in performance. The response varied across muscle groups. Alterations in muscle activation may lead to an increase in fluctuations in motor output after bed rest.

Publication Types:

PMID: 12832434 [PubMed - indexed for MEDLINE]

26: Percept Mot Skills. 2003 Aug;97(1):319-37.

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Influence of mental practice on development of voluntary control of a novel motor acquisition task.

Creelman J.

Department of Physical and Occupational Therapy, Idaho State University, Pocatello 83209, USA. creejame@isu.edu

The purpose of this investigation was to assess whether mental practice facilitates the development of voluntary control over the recruitment of the abductor hallucis muscle to produce isolated big toe abduction. A sample of convenience of 15 women and 20 men with a mean age of 28.8 yr. (SD=5.7) and healthy feet, who were unable voluntarily to abduct the big toe, were randomly assigned to one of three groups, a mental practice group, a physical practice group, and a group who performed a control movement during practice. Each subject received neuromuscular electrical stimulation to introduce the desired movement prior to each of five practice bouts over a single session lasting 2 hr. Big toe abduction active range of motion and surface electromyographic (EMG) output of the abductor hallucis and extensor digitorum brevis muscles were measured prior to the first practice bout and following each practice bout, yielding seven acquisition trials. Acquisition is defined as an improvement in both active range of motion and in the difference between the integrated EMG of the abductor hallucis and extensor digitorum brevis muscles during successive acquisition trials. Seven members of both the mental and physical practice groups and one member of the control group met the acquisition criteria. Chi-square analysis indicated the group difference was statistically significant, suggesting mental practice was effective for this task.

Publication Types:

PMID: 14604055 [PubMed - indexed for MEDLINE]

27: Percept Mot Skills. 2003 Aug;97(1):141-6.

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Knowledge and imagery of contractile mechanisms do not improve muscle strength.

Lorenzo J, Ives JC, Sforzo GA.

Department of Exercise and Sport Sciences, Ithaca College, NY 14850, USA.

Improving performance in strength tasks requires modifications charateristic of motor skill learning, such as more efficacious motor-unit firing behavior. Because domain-specific knowledge is integral to learning and performing motor kills, the present purpose was to examine selected factors of strength-specific knowledge and effects they might have on acquiring strength. Following baseline testing for maximal strength on a knee-extension task, participants were matched by sex and strength and placed into control (n=8) and treatment (n=8) groups. Quadriceps muscle electromyographic data were also collected. The treatment group underwent two educational sessions detailing muscle physiology, neural control of muscle force, and imagery training using this knowledge. The control group underwent two educational sessions about health and fitness. Following the educational sessions the participants were retested for strength. Analysis indicated that the education and imagery treatment had no effect on strength, nor did electromyographic measures indicate that the treatment group benefitted from intervention. It was concluded that the knowledge was simply not relevant to knee extension-force production or that use of the knowledge involved a disadvantageous internal focus of attention away from relevant task demands.

Publication Types:

PMID: 14604034 [PubMed - indexed for MEDLINE]

28: J Neurophysiol. 2003 Jul;90(1):300-12. Epub 2003 Mar 12.

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Human brain activation during sustained and intermittent submaximal fatigue muscle contractions: an FMRI study.

Liu JZ, Shan ZY, Zhang LD, Sahgal V, Brown RW, Yue GH.

Department of Biomedical Engineering, the Lerner Research Institute, The Cleveland Clinic Foundation, Ohio 44195, USA.

During prolonged submaximal muscle contractions, electromyographic (EMG) signals typically increase as a result of increasing motor unit activities to compensate for fatigue-induced force loss in the muscle. It is thought that cortical signals driving the muscle to higher activation levels also increases, but this has never been experimentally demonstrated. The purpose of this study was to quantify brain activation during submaximal fatigue muscle contractions using functional magnetic resonance imaging (fMRI). Twelve volunteers performed a sustained handgrip contraction for 225 s and 320 intermittent handgrip contractions ( approximately 960 s) at 30% maximal level while their brain was imaged. For the sustained contraction, EMG signals of the finger flexor muscles increased linearly while the target force was maintained. The fMRI-measured cortical activities in the contralateral sensorimotor cortex increased sharply during the first 150 s, then plateaued during the last 75 s. For the intermittent contractions, the EMG signals increased during the first 660 s and then began to decline, while the handgrip force also showed a sign of decrease despite maximal effort to maintain the force. The fMRI signal of the contralateral sensorimotor area showed a linear rise for most part of the task and plateaued at the end. For both the tasks, the fMRI signals in the ipsilateral sensorimotor cortex, prefrontal cortex, cingulate gyrus, supplementary motor area, and cerebellum exhibited steady increases. These results showed that the brain increased its output to reinforce the muscle for the continuation of the performance and possibly to process additional sensory information.

Publication Types:

PMID: 12634278 [PubMed - indexed for MEDLINE]

29: Scand J Med Sci Sports. 2003 Jun;13(3):159-68.

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Recovery of skeletal muscle contractility and hormonal responses to strength exercise after two weeks of high-volume strength training.

Raastad T, Glomsheller T, Bjøro T, Hallén J.

The Norwegian University of Sport and Physical Education, PO Box 4014 US, N-0806 Oslo, Norway, Hormone Laboratory, Aker Hospital, N-0514 Oslo, Norway. trulsr@nih.no

Exercise induced neuromuscular fatigue, recovery and hormonal responses were studied before (R1) and after (R2) 2 weeks of heavy strength training. Seventeen weight-trained male students were recruited into a heavy training group (HT, n = 10) and a control group (n = 7). During heavy training HT exercised leg extensors every day while control group exercised twice a week. Test workouts (R1 and R2) were used to induce neuromuscular fatigue and hormonal responses. Acute fatigue after the test workouts was reduced after heavy training in the HT group (P < 0.05) but not in the control group. Twenty-two hrs after the test workouts recovery from fatigue was not complete before heavy training, but recovery was complete after heavy training in both groups. The relative change in exercise induced cortisol and GH response, from before to after heavy training, was significantly different between groups, but for both hormones alterations in the control groups response was responsible for the between groups difference. IGF-1 concentration was reduced 22 h after the test workout performed after heavy training in the HT group (P < 0.05). In conclusion, two weeks of high volume strength training attenuated neuromuscular fatigue after a test workout with only minor changes in exercised induced hormone response.

Publication Types:

PMID: 12753488 [PubMed - indexed for MEDLINE]

30: J Clin Endocrinol Metab. 2003 Apr;88(4):1478-85.

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Testosterone dose-dependently increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension.

Storer TW, Magliano L, Woodhouse L, Lee ML, Dzekov C, Dzekov J, Casaburi R, Bhasin S.

Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, California 90059, USA. tostorer@cdrewu.edu

Testosterone supplementation in men increases fat-free mass, but whether measures of muscle performance, such as maximal voluntary strength, power, fatigability, or specific tension, are improved has not been determined. Furthermore, the extent to which these measures of muscle performance are related to testosterone dose or circulating concentration is unknown. To examine the relationship between testosterone dose and muscle performance, 61 healthy, eugonadal young men (aged 18-35 yr) were randomized to 1 of 5 groups, each receiving a long-acting GnRH agonist to suppress endogenous testosterone production plus weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate for 20 wk. These doses produced mean nadir testosterone concentrations of 253, 306, 542, 1345, and 2370 ng/dl, respectively. Maximal voluntary muscle strength and fatigability were determined by a seated leg press exercise. Leg power was measured using a validated leg power instrument. Specific tension was estimated by the ratio of one repetition maximum muscle strength to thigh muscle volume determined by magnetic resonance imaging. Testosterone administration was associated with a dose-dependent increase in leg press strength and leg power, but muscle fatigability did not change significantly during treatment. Changes in leg press strength were significantly correlated with total (r = 0.46; P = 0.0005) and free (r = 0.38; P = 0.006) testosterone as was leg power (total testosterone: r = 0.38; P = 0.007; free testosterone: r = 0.35; P = 0.015), but not muscle fatigability. Serum IGF-I concentrations were not significantly correlated with leg strength, power, or fatigability. Specific tension did not change significantly at any dose. We conclude that the effects of testosterone on muscle performance are specific; it increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. The changes in leg strength and power are dependent on testosterone dose and circulating testosterone concentrations and exhibit a log-linear relationship with serum total and free testosterone. Failure to observe a significant testosterone dose relationship with fatigability suggests that testosterone does not affect this component of muscle performance and that different components of muscle performance are regulated by different mechanisms.

Publication Types:

PMID: 12679426 [PubMed - indexed for MEDLINE]

31: Sports Med. 2003;33(1):47-58.

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'Psyching-up' and muscular force production.

Tod D, Iredale F, Gill N.

Centre for Rehabilitation, Exercise and Sport Science, School of Human Movement, Recreation and Performance, Victoria University, Melbourne, Victoria, Australia. david.tod1@research.vu.edu.au

Psyching-up refers to self-directed cognitive strategies used immediately prior to or during skill execution that are designed to enhance performance. This review focuses on research that has investigated the effect of psyching-up on force production; specifically, strength, muscular endurance and power. Although firm conclusions are not possible, the research tentatively suggests that psyching-up may enhance performance during dynamic tasks requiring strength and/or muscular endurance. However, more research is required. Power has received scant empirical attention and there are not enough data to support any conclusions. Preparatory arousal appears to be the most effective strategy although other strategies like imagery, self-talk and attentional focus also have empirical support. The range of tasks that have been used to measure force production have been limited to movements such as handgrip, leg extension, bench press, sit-ups, press-ups, pull-ups, and the standing broad jump. Additionally, most studies have used undergraduate and/or untrained samples. Only a very small number of studies have examined well-trained individuals. Currently, no explanation for why psyching-up may influence force production has any substantive support. Although a small number of studies have examined moderating and mediating variables, few consistent patterns have emerged and knowledge in this area is somewhat restricted. Given the importance that many athletes place on their mental preparation just prior to performance this is an area that warrants further examination. Research needs to examine a range of complex sport-specific tasks and use well-trained samples. Additionally, research needs to further examine why psyching-up may enhance force production.

Publication Types:

PMID: 12477377 [PubMed - indexed for MEDLINE]

32: J Gerontol A Biol Sci Med Sci. 2002 Mar;57(3):M168-72.

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Anaerobic power and physical function in strength-trained and non-strength-trained older adults.

Slade JM, Miszko TA, Laity JH, Agrawal SK, Cress ME.

Department of Exercise Science, University of Georgia, Athens 30602, USA. jslade@ceo.uga.edu

BACKGROUND: Challenging daily tasks, such as transferring heavy items or rising from the floor, may be dependent on the ability to generate short bursts of energy anaerobically. The purposes of this study were to determine if strength-trained (ST) older adults have higher anaerobic power output compared with non-strength-trained (NST) older adults and to determine the relationship between anaerobic power and performance-based physical function. METHODS: Thirty-five men and women (age 71.5 +/- 6.4 years, mean +/- SD; NST: n = 18, ST: n = 17) were grouped by training status. Outcome variables included relative anaerobic power (Wingate test), physical function measured with the Continuous Scale Physical Functional Performance Test (CS-PFP, scaled 0 to 100), and anthropometric lean thigh volume (LTV). Analysis of covariance (with age and sex as covariates) was used to determine group differences in the dependent variables listed above. Pearson's r was used to determine the relationship between anaerobic power, CS-PFP total score (TOT), and CS-PFP lower body strength domain score (LBS). RESULTS: The ST group had significantly higher mean anaerobic power (NST 58.9 +/- 16 W/l, ST 96.3 +/- 23 W/l), CS-PFP total (NST 61.2 +/- 13, ST 73.7 +/- 8), and LBS (NST 54.1 +/- 17, ST 70.9 +/- 8) compared with the NST group (p <.05). However, LTV was similar for both groups (NST 3.323 +/- 0.75; ST 3.179 +/- 0.79), which suggests that the ST group had higher muscle quality compared with the NST group. Anaerobic power was significantly related to TOT (r =.611, p =.001) and LBS (r =.650, p =.001). CONCLUSIONS: High levels of physical function in ST older adults may in part be explained by higher levels of anaerobic power associated with strength training.

Publication Types:

Research Support, Non-U.S. Gov't

PMID: 11867653 [PubMed - indexed for MEDLINE]

: The effects of strength training, cardiovascular training and their combination on flexibility of inactive older adults.

Fatouros IG, Taxildaris K, Tokmakidis SP, Kalapotharakos V, Aggelousis N, Athanasopoulos S, Zeeris I, Katrabasas I.

Democritus University of Thrace, Dept. of Physical Education & Sport Science, Komotini, Greece. fatouros@otenet.gr

The purpose of this study was to investigate the effects of aerobic training, strength training and their combination on joint range of motion of inactive older individuals. Thirty-two inactive older men (65 - 78 yr) were assigned to one of four groups (n = 8 per group): control (C), strength training (ST), cardiovascular training (CT), and combination of strength and aerobic training (SA). Subjects in the S, A, and SA trained three times a week for 16 weeks. ST included 10 resistance exercises for the major muscle groups at an intensity of 55 - 80% of 1-RM and CT included walking/jogging at 50 - 80 % of maximal heart rate. Body weight and height, physical activity level and maximal oxygen uptake (.VO(2)max) were measured before the training period. Isokinetic (60 and 180 deg x sec(-1)) and concentric strength (1-RM in bench and leg press) were assessed prior to and at the end of the training period. Hip flexion, extension, abduction, and adduction, shoulder extension, flexion, and adduction, knee flexion, elbow flexion and sit-and-reach score were determined before and at 8 and 16 weeks of training. There were no differences between groups in .VO(2)max, body weight, and height (p < 0.05). ST and SA but not CT and C increased isokinetic and concentric strength at the end of the training period (p < 0.05). ST and SA increased significantly (p < 0.05) sit-and-reach performance, elbow flexion, knee flexion, shoulder flexion and extension and hip flexion and extension both at mid- and post-training. CT increased (p < 0.05) only hip flexion and extension at post training. Results indicate that resistance training may be able to increase range of motion of a number of joints of inactive older individuals possibly due to an improvement in muscle strength.

PMID: 11842358 [PubMed - indexed for MEDLINE]

34: Acta Physiol Scand. 1998 Aug;163(4):361-8.

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Effects of real and imagined training on voluntary muscle activation during maximal isometric contractions.

Herbert RD, Dean C, Gandevia SC.

Prince of Wales Medical Research Institute, University of New South Wales, Australia.

In this study we directly tested the hypothesis that isometric strength training increases voluntary drive to muscles. In addition, it was attempted to replicate the findings of an earlier study that showed imagined training increases voluntary strength as much as actual training, as this finding provides key support for the hypothesis that training increases voluntary drive (Yue & Cole 1992). Fifty-four subjects were randomly allocated to groups that performed 8 weeks of isometric training of the elbow flexor muscles, imagined isometric training, or a control task involving the lower limbs. Voluntary isometric strength and activation of the elbow flexor muscles were measured before and after training. Voluntary activation was measured with a sensitive form of twitch interpolation. Training, imagined training and control groups increased voluntary isometric elbow flexor strength by means of 17.8% (+/- 3.1 SEM), 6.8% (+/- 2.6) and 6.5% (+/- 3.0), respectively. The training group increased in strength significantly more than imagined training and control groups (P = 0.01 for both comparisons), but the small difference between imagined training and control groups was not significant (P = 0.31). Prior to training, voluntary activation of all subjects was high (96.2 +/- 0.5%). This did not change significantly with training and there were no significant differences between groups. These data challenge the hypothesis that training of the elbow flexor muscles increases isometric strength by inducing adaptations of the central nervous system, because they show that training does not increase voluntary activation and imagined training does not increase strength.

Publication Types:

PMID: 9789579 [PubMed - indexed for MEDLINE]

35: Can J Appl Physiol. 1997 Aug;22(4):328-36.

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Effects of combined training loads on relations among force, velocity, and power development.

Toji H, Suei K, Kaneko M.

Laboratory of Health and Sport Science, Faculty of Liberal Arts, Himeji Institute of Technology, Hyogo, Japan.

The effects of different training programs on the force-velocity relation and the maximum power output from the elbow flexor muscles were examined in 12 male adults. The subjects were divided into two equal groups (G30 + 100 and G30 + 0). In the G30 + 100 group, training was performed with five repetitions at 30% maximum strength (Fmax) and five isometric contractions (100% Fmax), and in the G30 + 0 group with five repetitions at 30% Fmax and five contractions with no load (0% Fmax). Training was performed 3 days a week for 11 weeks. Maximum power increased significantly in both groups after training. The power increase was significantly greater in the G30 + 100 group. Maximum strength was significantly higher only in the G30 + 100 group, while maximum velocity increased in both groups. No significant difference in strength or velocity gain was observed between the two groups. These results suggest that isometric training at maximum strength (100% Fmax) is a more effective form of supplementary training to increase power production than no load training at maximum velocity.

Publication Types:

PMID: 9263617 [PubMed - indexed for MEDLINE]

36: J Neurophysiol. 1992 May;67(5):1114-23.

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Strength increases from the motor program: comparison of training with maximal voluntary and imagined muscle contractions.

Yue G, Cole KJ.

Department of Exercise Science, University of Iowa, Iowa City 52242.

1. This study addressed potential neural mechanisms of the strength increase that occur before muscle hypertrophy. In particular we examined whether such strength increases may result from training-induced changes in voluntary motor programs. We compared the maximal voluntary force production after a training program of repetitive maximal isometric muscle contractions with force output after a training program that did not involve repetitive activation of muscle; that is, after mental training. 2. Subjects trained their left hypothenar muscles for 4 wk, five sessions per week. One group produced repeated maximal isometric contractions of the abductor muscles of the fifth digit's metacarpophalangeal joint. A second group imagined producing these same, effortful isometric contractions. A third group did not train their fifth digit. Maximal abduction force, flexion/extension force and electrically evoked twitch force (abduction) of the fifth digit were measured along with maximal integrated electromyograms (EMG) of the hypothenar muscles from both hands before and after training. 3. Average abduction force of the left fifth digit increased 22% for the Imagining group and 30% for the Contraction group. The mean increase for the Control group was 3.7%. 4. The maximal abduction force of the right (untrained) fifth digit increased significantly in both the Imagining and Contraction groups after training (10 and 14%, respectively), but not in the Control group (2.3%). These results are consistent with previous studies of training effects on contralateral limbs. 5. The abduction twitch force evoked by supramaximal electrical stimulations of the ulnar nerve was unchanged in all three groups after training, consistent with an absence of muscle hypertrophy. The maximal force of the left great toe extensors for individual subjects remained unchanged after training, which argues against strength increases due to general increases in effort level. 6. Increases in abduction and flexion forces of the fifth digit were poorly correlated in subjects of both training groups. The fifth finger abduction force and the hypothenar integrated EMG increases were not well correlated in these subjects either. Together these results indicate that training-induced changes of synergist and antagonist muscle activation patterns may have contributed to force increases in some of the subjects. 7. Strength increases can be achieved without repeated muscle activation. These force gains appear to result from practice effects on central motor programming/planning. The results of these experiments add to existing evidence for the neural origin of strength increases that occur before muscle hypertrophy.

Publication Types:

PMID: 1597701 [PubMed - indexed for MEDLINE]