Combined isometric, concentric, and eccentric resistance exercise prevents unloading-induced muscle atrophy in rats

Previously, we reported that an isometric resistance training program that was effective in stimulating muscle hypertrophy in ambulatory rats could not completely prevent muscle atrophy during unloading (Haddad F, Adams GR, Bodell PW, Baldwin KM. J Appl Physiol 100: 433–441, 2006). These results indicated that preventing muscle atrophy does not appear to be simply a function of providing an anabolic stimulus. The present study was undertaken to determine if resistance training, with increased volume (3-s contractions) and incorporating both static and dynamic components, would be effective in preventing unloading-induced muscle atrophy. Rats were exposed to 5 days of muscle unloading via tail suspension. During that time one leg received electrically stimulated resistance exercise (RE) that included an isometric, concentric, and eccentric phase. The results of this study indicate that this combined-mode RE provided an anabolic stimulus sufficient to maintain the mass and myofibril content of the trained but not the contralateral medial gastrocnemius (MG) muscle. Relative to the contralateral MG, the RE stimulus increased the amount of total RNA (indicative of translational capacity) as well as the mRNA for several anabolic/myogenic markers such as insulin-like growth factor-I, myogenin, myoferlin, and procollagen III-α-1 and decreased that of myostatin, a negative regulator of muscle size. The combined-mode RE protocol also increased the activity of anabolic signaling intermediates such as p70S6 kinase. These results indicate that a combination of static- and dynamic-mode RE of sufficient volume provides an effective stimulus to stimulate anabolic/myogenic mechanisms to counter the initial stages of unloading-induced muscle atrophy.

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Resistance Exercise-Induced Apelin Is Not Modulated by Higher Dietary Protein Density in Overweight Adults

Current Developments in Nutrition ◽

10.1093/cdn/nzaa040_050 ◽

2020 ◽

Vol 4 (Supplement_2) ◽

pp. 50-50

Author(s):

Colleen McKenna ◽

Amadeo Salvador ◽

Alexander Keeble ◽

Rafael Alamilla ◽

Susannah Scaroni ◽

...

Keyword(s):

Resistance Training ◽

Muscle Strength ◽

Resistance Exercise ◽

Dietary Protein ◽

Middle Aged ◽

Resistance Training Program ◽

Exercise Induced ◽

Protein Density ◽

Middle Aged Adults ◽

Plasma Apelin

Abstract Objectives Apelin is a putative exercise-sensitive myokine that has been shown to be associated with physical independence during aging. Physical performance is highly dependent on muscle strength, with a clear role of dietary protein (i.e., > Recommended Dietary Allowance) for the maintenance of age-related muscle strength. However, the influence of dietary protein density on exercise-induced apelin remains unknown. Therefore, our aim was to evaluate plasma apelin concentrations and its relationship with muscle strength in middle-aged adults consuming differential amounts of animal-based protein during progressive resistance training. Methods 41 overweight middle-aged adults (50 ± 2 y, BMI 28 ± 1 kg · m−2, M = 19, F = 22) were stratified and randomized to consume either high protein (1.68 ± 0.06 g · kg−1·d−1) or moderate amounts of animal-based protein (1.16 ± 0.04 g · kg−1·d−1) during a 10-week weight-maintenance nutrition counseling-controlled resistance training program. Body composition was assessed by dual-energy x-ray absorptiometry. Muscle strength was assessed by one-repetition maximum (1RM) and isometric maximal voluntary contraction (MVC) at 60° knee angle. Oral glucose tolerance tests were performed at baseline and post-intervention. Results Main effects of time were observed for increases in lean body mass (P = 0.003), upper and lower body 1RM (all P ≤ 0.001), isometric MVC (P = 0.013), and plasma apelin concentrations (P = 0.007). There were no changes in body adiposity or glucose-insulin regulation (e.g., HOMA-IR, Matsuda) with the intervention (all P ≥ 0.152). Apelin was positively and significantly associated with isometric MVC (extension: r = 0.233, P = 0.047; flexion: r = 0.308, P = 0.008), but not 1RM. Conclusions Our results show that resistance training increases circulating apelin concentrations which is related to isometric strength gain. However, higher consumption of animal-based protein foods does not potentiate these resistance-exercise induced adaptations in overweight middle-aged adults. Funding Sources Funded in part by the Beef Checkoff. CFM funded by JBT Fellowship, UIUC.

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Animal model for progressive resistance exercise: a detailed description of model and its implications for basic research in exercise

Motriz Revista de Educação Física ◽

10.1590/s1980-65742013000100018 ◽

2013 ◽

Vol 19 (1) ◽

pp. 178-184 ◽

Cited By ~ 8

Author(s):

Ricardo Cardoso Cassilhas ◽

Ismair Teodoro Reis ◽

Daniel Venâncio ◽

Jansen Fernandes ◽

Sérgio Tufik ◽

...

Keyword(s):

Resistance Training ◽

Resistance Exercise ◽

Electric Shock ◽

Negative Reinforcement ◽

Control Group ◽

Progressive Resistance Training ◽

Resistance Training Program ◽

Experimental Group ◽

Progressive Resistance Exercise ◽

Progressive Resistance

The Several animal models have been proposed for resistance training. In addition, the results of these studies have been highly variable. Some of the studies have used negative reinforcement, electric shock or food deprivation to motivate the learning of the task. Features such as conditioning through electric shock may undermine the significance of the results or even prevent the model from being successfully executed. Due to these reasons, in this study we propose to use an adaptation of the vertical ladder climbing model for progressive resistance training in rats, albeit with a unique feature to ensure the homogeneity of the study groups: a period of adaptation to the apparatus without any negative reinforcement followed by a subsequent pairing of animals based on their ability to learn. The animals were distributed in the experimental group who were subjected to 8 weeks of a progressive resistance exercise protocol and the control group. After 8wks, the gastrocnemius, soleus, flexor digitorum longus (FDL), and plantaris muscles were removed and the cross-sectional area morphometry was obtened. The animals from experimental group showed hypertrophy [F(4, 15)=17,404, P < 0.001] for gastrocnemius [60% of hipertrophy; Control (2628,64 ± 348,50) versus Experimental (4207,77 ± 1256,52); ES=1.96; Power=0,86]; FDL [35% of hipertrophy; Control (2753,80 ± 359,54) versus Experimental (3711,84 ± 279,45); ES=2.99; Power=0.99] and plantaris [38% of hipertrophy; Control (2730,44 ± 320,56) versus Experimental (3767,30 ± 625,80); ES=2.19; Power=0.92], without modifications for soleus. All animals successfully completed the 8-week progressive resistance training program without any injuries, abandonment or death. Negative reinforcements such as electric shock were not required at any time in the experiment. In conclusion, we showed an adaptation of the previus model for progressive resistance training in rats. A period of adaptation to the apparatus without any negative reinforcement followed by a subsequent pairing of animals based on their ability to learn may be a alternative strategy for the original protocol. We also observed hypertrophy (gastrocnemius, FDL, and plantaris) showed the vality of this procolos for resistance exercise issues. The results of this study may be useful in basic/ applied neuroscience research and resistance exercise.

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PO-306 The effect of four weeks hypoxic resistance training on myostatin and follistatin expression in skeletal muscle of rats

Exercise Biochemistry Review ◽

10.14428/ebr.v1i5.13393 ◽

2018 ◽

Vol 1 (5) ◽

Author(s):

Xuecheng Bai Bai ◽

Yang Hu ◽

Yanchun Li

Keyword(s):

Skeletal Muscle ◽

Resistance Training ◽

Resistance Exercise ◽

Mrna Expression ◽

Muscle Atrophy ◽

Biceps Brachii ◽

Skeletal Muscle Atrophy ◽

Significant Difference ◽

Wet Weight ◽

Hypoxic Resistance

Objective Loss of skeletal muscle weight is a common phenomenon in hypoxic environment. It has been recognized that resistance training can reduce hypoxia-induced skeletal muscle atrophy, but its molecular mechanism is still unclear. Myostatin is a major factor that inhibits muscle growth and differentiation, and Follistatin can inhibit Myostatin. Therefore, this study is to clarify the effect of 4-week hypoxic resistance exercise on Myostatin and Follistatin gene expression in skeletal muscle of rats. Methods Twenty four 8-week-old male SD rats were randomly divided into normoxic control group (group C: 6 rats), normoxic exercise group (group R: 6 rats), hypoxic control group (group H: 6 rats) and hypoxic exercise group (group HR: 6 rats). Rats in each hypoxic group were fed in a hypoxic chamber (atmospheric hypoxia) with oxygen concentration of 12.7% (simulated 4000m altitude). Rats in each exercise group were trained according to the rat's resistance training program developed in our laboratory. After all the intervention, DEXA was used to analyze the body composition. The soleus, extensor digitorum longus and biceps brachii muscles of rats were taken and the wet weight of individual muscles was measured. The data were processed by SPSS17.0 statistical software. The expression level of skeletal muscle mRNA was expressed as "median (25-75%)" and the data of body composition and muscle wet weight were expressed as"mean±standard deviation". The differences between the groups were evaluated using a one-way analysis of variance (ANOVA) test. The significance level for the study was less than 0.05. Results Body composition analysis after 4 weeks of hypoxic intervention showed that the body weight of rats in group H decreased significantly (p=0.012), and the muscle mass decreased more significantly (p<0.001). But resistance exercises obviously reduced the muscle atrophy (p<0.01) caused by hypoxia. After analyzing the changes of the wet weight of individual muscles, it was found that the wet weight of biceps brachii in HR group was significantly higher than that in H group (p=0.048). After 4 weeks of hypoxic intervention and hypoxic resistance exercise, the expression of Myostatin mRNA in individual muscles of each group changed differently. The expression of Myostatin mRNA in soleus muscle of H group was significantly higher than that of C group (371.2%) after 4 weeks of hypoxia intervention. Myostatin mRNA expression in soleus and biceps brachii of HR group was significantly lower than that of H group (591.1% and 478.4% respectively). However, there was no significant difference in the expression level of Myostatin mRNA in the extensor digitorum longus between each group (p=0.259). The change of Follistatin mRNA expression in different groups also showed a different trend. The expression of Follistatin mRNA in soleus muscle and biceps brachii muscle was significantly different among groups (p=0.003, p=0.004, respectively). However, there was no significant difference in the expression level of Follistatin mRNA in the extensor digitorum longus between each group (p=0.734). Myostatin mRNA/Follistatin mRNA ratio (M/F) showed a more significant difference. The M/F ratio of soleus muscle in group H was significantly lower than that in group C (p<0.001), but the M/F ratio in group HR was significantly higher than that in group H (p<0.001). The M/F ratio of biceps brachii in group H was significantly lower than that in group C (p<0.001), but the M/F ratio in group HR showed a higher trend than that in group H (p=0.051). Conclusions Hypoxic exposure results in an increase in Myostatin mRNA expression in skeletal muscle, but hypoxic resistance exercise reduces such an increase. On the contrary, the level of Follistatin mRNA expression in skeletal muscle decreased after hypoxic exposure, and hypoxic resistance exercise could slow down the decline. As a result, rat resistance exercise significantly slowed down hypoxia-induced muscle atrophy. In conclusion, the mutual restriction between Myostatin and Follistatin is one of the main links of resistance exercise to reduce hypoxia-induced skeletal muscle atrophy. However, the process of resistance training to reduce the hypoxia-induced skeletal muscle atrophy is very complex. There are many molecular signaling pathways involved, which need further study.

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Acute and chronic resistance training downregulates select LINE-1 retrotransposon activity markers in human skeletal muscle

AJP Cell Physiology ◽

10.1152/ajpcell.00192.2017 ◽

2018 ◽

Vol 314 (3) ◽

pp. C379-C388 ◽

Cited By ~ 4

Author(s):

Matthew A. Romero ◽

C. Brooks Mobley ◽

Petey W. Mumford ◽

Paul A. Roberson ◽

Cody T. Haun ◽

...

Keyword(s):

Skeletal Muscle ◽

Resistance Training ◽

Resistance Exercise ◽

Satellite Cell ◽

Vastus Lateralis ◽

Future Research ◽

Resistance Training Program ◽

Myoblast Proliferation ◽

Retrotransposon Activity

Herein, we examined if acute or chronic resistance exercise affected markers of skeletal muscle long interspersed nuclear element-1 (LINE-1) retrotransposon activity. In study 1, 10 resistance-trained college-aged men performed three consecutive daily back squat sessions, and vastus lateralis biopsies were taken before (Pre), 2 h following session 1 (Post1), and 3 days following session 3 (Post2). In study 2, 13 untrained college-aged men performed a full-body resistance training program (3 days/wk), and vastus lateralis biopsies were taken before ( week 0) and ~72 h following training cessation ( week 12). In study 1, LINE-1 mRNA decreased 42–48% at Post1 and 2 ( P < 0.05), and reverse transcriptase (RT) activity trended downward at Post2 (−37%, P = 0.067). In study 2, LINE-1 mRNA trended downward at week 12 (−17%, P = 0.056) while LINE-1 promoter methylation increased (+142%, P = 0.041). Open reading frame (ORF)2p protein expression (−24%, P = 0.059) and RT activity (−26%, P = 0.063) also trended downward by week 12. Additionally, changes in RT activity versus satellite cell number were inversely associated ( r = −0.725, P = 0.008). Follow-up in vitro experiments demonstrated that 48-h treatments with lower doses (1 μM and 10 μM) of efavirenz and nevirapine (non-nucleoside RT inhibitors) increased myoblast proliferation ( P < 0.05). However, we observed a paradoxical decrease in myoblast proliferation with higher doses (50 μM) of efavirenz and delavirdine. This is the first report suggesting that resistance exercise downregulates markers of skeletal muscle LINE-1 activity. Given our discordant in vitro findings, future research is needed to thoroughly assess whether LINE-1-mediated RT activity enhances or blunts myoblast, or primary satellite cell, proliferative capacity.

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Myostatin reduces Akt/TORC1/p70S6K signaling, inhibiting myoblast differentiation and myotube size

AJP Cell Physiology ◽

10.1152/ajpcell.00105.2009 ◽

2009 ◽

Vol 296 (6) ◽

pp. C1258-C1270 ◽

Cited By ~ 426

Author(s):

Anne Ulrike Trendelenburg ◽

Angelika Meyer ◽

Daisy Rohner ◽

Joseph Boyle ◽

Shinji Hatakeyama ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Atrophy ◽

Transforming Growth Factor ◽

Negative Regulator ◽

Bone Morphogenetic Protein 2 ◽

Muscle Size ◽

Skeletal Muscle Atrophy ◽

Myoblast Differentiation ◽

Activin Receptor

Myostatin is a negative regulator of skeletal muscle size, previously shown to inhibit muscle cell differentiation. Myostatin requires both Smad2 and Smad3 downstream of the activin receptor II (ActRII)/activin receptor-like kinase (ALK) receptor complex. Other transforming growth factor-β (TGF-β)-like molecules can also block differentiation, including TGF-β1, growth differentiation factor 11 (GDF-11), activins, bone morphogenetic protein 2 (BMP-2) and BMP-7. Myostatin inhibits activation of the Akt/mammalian target of rapamycin (mTOR)/p70S6 protein synthesis pathway, which mediates both differentiation in myoblasts and hypertrophy in myotubes. Blockade of the Akt/mTOR pathway, using small interfering RNA to regulatory-associated protein of mTOR (RAPTOR), a component of TOR signaling complex 1 (TORC1), increases myostatin-induced phosphorylation of Smad2, establishing a myostatin signaling-amplification role for blockade of Akt. Blockade of RAPTOR also facilitates myostatin's inhibition of muscle differentiation. Inhibition of TORC2, via rapamycin-insensitive companion of mTOR (RICTOR), is sufficient to inhibit differentiation on its own. Furthermore, myostatin decreases the diameter of postdifferentiated myotubes. However, rather than causing upregulation of the E3 ubiquitin ligases muscle RING-finger 1 ( MuRF1) and muscle atrophy F-box ( MAFbx), previously shown to mediate skeletal muscle atrophy, myostatin decreases expression of these atrophy markers in differentiated myotubes, as well as other genes normally upregulated during differentiation. These findings demonstrate that myostatin signaling acts by blocking genes induced during differentiation, even in a myotube, as opposed to activating the distinct “atrophy program.” In vivo, inhibition of myostatin increases muscle creatine kinase activity, coincident with an increase in muscle size, demonstrating that this in vitro differentiation measure is also upregulated in vivo.

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ACTN3 genotype is associated with increases in muscle strength in response to resistance training in women

Journal of Applied Physiology ◽

10.1152/japplphysiol.01139.2004 ◽

2005 ◽

Vol 99 (1) ◽

pp. 154-163 ◽

Cited By ~ 174

Author(s):

Priscilla M. Clarkson ◽

Joseph M. Devaney ◽

Heather Gordish-Dressman ◽

Paul D. Thompson ◽

Monica J. Hubal ◽

...

Keyword(s):

Resistance Training ◽

Body Mass ◽

Biceps Brachii ◽

Elbow Flexor ◽

Muscle Performance ◽

Muscle Size ◽

P Value ◽

Ratio Test ◽

Cross Sectional ◽

Resistance Training Program

The α-actinin 3 (ACTN3) gene encodes a protein of the Z disk of myofibers, and a polymorphism of ACTN3 results in complete loss of the protein. The ACTN3 genotype (R577X) has been found to be associated with performance in Australian elite athletes (Yang N, MacArthur DG, Gulbin JP, Hahn AG, Beggs AH, Easteal S, and North K. Am J Hum Genet 73: 627–631, 2003). We studied associations between ACTN3 genotype and muscle size [cross-sectional area of the biceps brachii via magnetic resonance imaging (MRI)] and elbow flexor isometric (MVC) and dynamic [1-repetition maximum (1-RM)] strength in a large group of men ( N = 247) and women ( N = 355) enrolled in a 12-wk standardized elbow flexor/extensor resistance training program of the nondominant arm at one of eight study centers. We found no association between ACTN3 R577X genotype and muscle phenotype in men. However, women homozygous for the ACTN3 577X allele (XX) had lower baseline MVC compared with heterozygotes ( P < 0.05) when adjusted for body mass and age. Women homozygous for the mutant allele (577X) demonstrated greater absolute and relative 1-RM gains compared with the homozygous wild type (RR) after resistance training when adjusted for body mass and age ( P < 0.05). There was a trend for a dose-response with genotype such that gains were greatest for XX and least for RR. Significant associations were validated in at least one ethnic subpopulation (Caucasians, Asians) and were independent of training volume. About 2% of baseline MVC and of 1-RM strength gain after training were attributable to ACTN3 genotype (likelihood-ratio test P value, P = 0.01), suggesting that ACTN3 is one of many genes contributing to genetic variation in muscle performance and adaptation to exercise.

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Effects of Three Resistance Exercise Orders on Muscular Function and Body Composition in Older Women

International Journal of Sports Medicine ◽

10.1055/a-1192-5205 ◽

2020 ◽

Vol 41 (14) ◽

pp. 1024-1031

Author(s):

Márcia M. Dib ◽

Crisieli M. Tomeleri ◽

João Pedro Nunes ◽

Paolo M. Cunha ◽

Alex S. Ribeiro ◽

...

Keyword(s):

Body Composition ◽

Resistance Training ◽

Resistance Exercise ◽

Older Women ◽

Test Performance ◽

Muscular Strength ◽

Whole Body ◽

Functional Fitness ◽

Resistance Training Program ◽

Motor Tests

AbstractThe purpose of the present study was to compare the effects of three resistance exercise orders on muscular strength, body composition, and functional fitness in trained older women. Forty-five women (aged ≥60 years), after performing 12 weeks of a pre-conditioning resistance-training program were randomly assigned in one of the following groups that performed the exercises in the following orders: multi-joint to single-joint order (MJ-SJ, n=15), single-joint to multi-joint order (SJ-MJ, n=15), and alternating between upper and lower body order (ALT, n=15). Specific training intervention lasted 12 weeks (3x/week) and was composed of eight exercises performed in three sets of 15/10/5 repetitions, with increasing load through the sets. Muscular strength was estimated by one-repetition maximum tests; body composition was assessed by whole-body dual-energy x-ray absorptiometry, and functional fitness was analyzed with a sequence of four motor tests. All groups improved similarly in muscular strength (Cohen’s effect size: MJ-SJ=0.45; SJ-MJ=0.48; ALT=0.45), skeletal muscle mass (MJ-SJ=0.08; SJ-MJ=0.07; ALT=0.09), and functional test performance (MJ-SJ=0.38; SJ-MJ=0.20; ALT=0.31), but no change was observed for body fat (P>0.05). The results suggest that 12 weeks of resistance training induce positive changes in muscle morphofunctionality, regardless of the exercise order employed in trained older women.

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Short-Time β-Alanine Supplementation on the Acute Strength Performance after High-Intensity Intermittent Exercise in Recreationally Trained Men

Sports ◽

10.3390/sports7050108 ◽

2019 ◽

Vol 7 (5) ◽

pp. 108 ◽

Cited By ~ 1

Author(s):

Marcelo Conrado Freitas ◽

Jason Cholewa ◽

Valéria Panissa ◽

Giovanni Quizzini ◽

João Vitor de Oliveira ◽

...

Keyword(s):

Resistance Training ◽

Resistance Exercise ◽

Training Program ◽

High Intensity ◽

Intermittent Exercise ◽

Bioelectrical Impedance ◽

Fat Free Mass ◽

Resistance Training Program ◽

Strength Performance ◽

Leg Press

(1) Background: We investigated the effects of 28 days of beta-alanine (β-alanine) supplementation on the acute interference effect of high-intensity intermittent exercise (HIIE) on lower-body resistance exercise performance, body composition, and strength when combined with a resistance training program. (2) Methods: Twenty-two males were randomized into: β-alanine supplementation (6.4 g/day) or placebo (6.4 g/day maltodextrin) during 28 days. Total body water, intracellular and extracellular water, fat-free mass (FFM), and fat mass were assessed using bioelectrical impedance. Participants performed 5000-m HIIE (1:1 effort and rest ratio) followed by resistance exercise (four sets of 80% at 45° leg press until muscular failure) at baseline and after 28 days. The resistance training program consisted of three sets of 10 to 12 RM with 90 s of rest, four days per week. (3) Results: For the post-HIIE leg press volume, higher values were observed post-training than pre-training, but no group x time interaction was observed. There was a non-significant trend for an interaction in the FFM change (β-alanine = 2.8% versus placebo = 1.0%, p = 0.072). (4) Conclusion: Twenty-eight days of β-alanine supplementation did not prevent acute strength loss during resistance exercise after high-intensity interval exercise, nor increase strength or hypertrophic adaptations associated with resistance training.

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Resistance Training in Hypoxia as a New Therapeutic Modality for Sarcopenia—A Narrative Review

Life ◽

10.3390/life11020106 ◽

2021 ◽

Vol 11 (2) ◽

pp. 106

Author(s):

Won-Sang Jung ◽

Sung-Woo Kim ◽

Jeong-Weon Kim ◽

Hun-Young Park

Keyword(s):

Resistance Training ◽

Resistance Exercise ◽

Intracellular Signaling ◽

Exercise Intervention ◽

Muscle Size ◽

Therapeutic Modality ◽

Bodily Function ◽

Muscular Function ◽

Low Altitude

Hypoxic training is believed to be generally useful for improving exercise performance in various athletes. Nowadays, exercise intervention in hypoxia is recognized as a new therapeutic modality for health promotion and disease prevention or treatment based on the lower mortality and prevalence of people living in high-altitude environments than those living in low-altitude environments. Recently, resistance training in hypoxia (RTH), a new therapeutic modality combining hypoxia and resistance exercise, has been attempted to improve muscle hypertrophy and muscle function. RTH is known to induce greater muscle size, lean mass, increased muscle strength and endurance, bodily function, and angiogenesis of skeletal muscles than traditional resistance exercise. Therefore, we examined previous studies to understand the clinical and physiological aspects of sarcopenia and RTH for muscular function and hypertrophy. However, few investigations have examined the combined effects of hypoxic stress and resistance exercise, and as such, it is difficult to make recommendations for implementing universal RTH programs for sarcopenia based on current understanding. It should also be acknowledged that a number of mechanisms proposed to facilitate the augmented response to RTH remain poorly understood, particularly the role of metabolic, hormonal, and intracellular signaling pathways. Further RTH intervention studies considering various exercise parameters (e.g., load, recovery time between sets, hypoxic dose, and intervention period) are strongly recommended to reinforce knowledge about the adaptational processes and the effects of this type of resistance training for sarcopenia in older people.

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Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity

Journal of Applied Physiology ◽

10.1152/japplphysiol.90538.2008 ◽

2008 ◽

Vol 105 (5) ◽

pp. 1454-1461 ◽

Cited By ~ 128

Author(s):

L. Holm ◽

S. Reitelseder ◽

T. G. Pedersen ◽

S. Doessing ◽

S. G. Petersen ◽

...

Keyword(s):

Resistance Training ◽

Muscle Strength ◽

Resistance Exercise ◽

Muscle Hypertrophy ◽

Vastus Lateralis ◽

Load Resistance ◽

Muscle Size ◽

Heavy Load ◽

Cross Sectional ◽

Light Load

Muscle mass accretion is accomplished by heavy-load resistance training. The effect of light-load resistance exercise has been far more sparsely investigated with regard to potential effect on muscle size and contractile strength. We applied a resistance exercise protocol in which the same individual trained one leg at 70% of one-repetition maximum (1RM) (heavy load, HL) while training the other leg at 15.5% 1RM (light load, LL). Eleven sedentary men (age 25 ± 1 yr) trained for 12 wk at three times/week. Before and after the intervention muscle hypertrophy was determined by magnetic resonance imaging, muscle biopsies were obtained bilaterally from vastus lateralis for determination of myosin heavy chain (MHC) composition, and maximal muscle strength was assessed by 1RM testing and in an isokinetic dynamometer at 60°/s. Quadriceps muscle cross-sectional area increased ( P < 0.05) 8 ± 1% and 3 ± 1% in HL and LL legs, respectively, with a greater gain in HL than LL ( P < 0.05). Likewise, 1RM strength increased ( P < 0.001) in both legs (HL: 36 ± 5%, LL: 19 ± 2%), albeit more so with HL ( P < 0.01). Isokinetic 60°/s muscle strength improved by 13 ± 5% ( P < 0.05) in HL but remained unchanged in LL (4 ± 5%, not significant). Finally, MHC IIX protein expression was decreased with HL but not LL, despite identical total workload in HL and LL. Our main finding was that LL resistance training was sufficient to induce a small but significant muscle hypertrophy in healthy young men. However, LL resistance training was inferior to HL training in evoking adaptive changes in muscle size and contractile strength and was insufficient to induce changes in MHC composition.

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