Performance Area > Peer Reviewed Studies Discussion

Muscle Architecture

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RJ Nelsen:
Yeah. I'm thinking about writing an article around that article and other one's saying similar things. Something about training specificity regarding the type of muscular contraction.

adarqui:

--- Quote from: RJ Nelsen on June 08, 2009, 04:02:16 pm ---Yeah. I'm thinking about writing an article around that article and other one's saying similar things. Something about training specificity regarding the type of muscular contraction.

--- End quote ---

nice..

adarqui:
Myosin heavy chain IIX overshoot in human skeletal muscle

Abstract
The distribution of myosin heavy chain (MHC) isoforms, fiber type composition, and fiber size of the vastus lateralis muscle were analyzed by sodium dodecylsulfate polymerase gel electrophoresis (SDS-PAGE), ATPase histochemistry, and immunocytochemistry in a group of adult sedentary men before and after 3 months of heavy-load resistance training and, subsequently, after 3 months of detraining. Following the period of resistance training, MHC IIX content decreased from 9.3 ± 2.1% to 2.0 ± 0.8% (P < 0.01), with a corresponding increase in MHC IIA (42.4 ± 3.9% vs. 49.6 ± 4.0% [P < 0.05]). Following detraining the amount of MHC IIX reached values that were higher than before and after resistance training (17.2 ± 3.2% [P < 0.01]). Changes in fiber type composition resembled the changes observed in MHC isoform content. Significant hypertrophy was observed for the type II fibers after resistance training. Maximal isometric quadriceps strength increased after resistance training, but returned to pretraining levels after detraining. The present results suggest that heavy-load resistance training decreases the amount of MHC IIX while reciprocally increasing MHC IIA content. Furthermore, detraining following heavy-load resistance training seems to evoke an overshoot in the amount of MHC IIX to values markedly higher than those observed prior to resistance training. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 1095-1104, 2000







Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining
Lars L. Andersen,1,2 Jesper L. Andersen,2 S. Peter Magnusson,1 Charlotte Suetta,1 Jørgen L. Madsen,2 Lasse R. Christensen,2 and Per Aagaard1

1Institute of Sports Medicine Copenhagen/Team Danmark Testcenter, Bispebjerg Hospital, and 2Copenhagen Muscle Research Center, Rigshospitalet, Copenhagen, Denmark

Submitted 26 January 2005 ; accepted in final form 22 February 2005

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°/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.








Upper body training and the triceps brachii muscle of elite cross country skiers.

Original Article
Scandinavian Journal of Medicine & Science in Sports. 16(2):121-126, April 2006.
Terzis, G. 1; Stattin, B. 2; Holmberg, H-C. 3

Abstract:
This study aimed at evaluating whether addition of extensive upper body training in well-trained cross country skiers induces an adaptation of the triceps brachii (TB) muscle and whether this affects performance. Muscle biopsies were obtained from TB muscle in six male elite cross country skiers before and after 20 weeks of increased upper body training. The cross-sectional area of type I and IIA fibers increased by 11.3% and 24.0%, respectively, and so did the number of capillaries per fiber (2.3-3.2) (all P<0.05). SDS-polyacrylamide electrophoresis revealed in single fibers that the number of fibers expressing myosin heavy chain (MHC) type I isoform decreased from 68.7% to 60.9% (P<0.05), MHC I/IIA isoform was unaltered, while MHC IIA fibers increased from 21.6% to 35.7% and the 4.8% MHC IIA/IIX disappeared with the training (both P<0.05). Citrate synthase and 3-hydroxyacyl coenzyme A dehydrogenase activities increased by 23.3% and 15.4%, respectively, and double poling 10 km time-trial by 10.4% (all P<0.05). The values for TB are similar to what has been demonstrated for leg muscles after exercise training. The subjects who demonstrated the largest improvement in performance exhibited the largest muscle adaptation, which, in turn, was related to the pre-maximal oxygen uptake.









Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity
L. Holm,1 S. Reitelseder,1 T. G. Pedersen,1 S. Doessing,1 S. G. Petersen,1 A. Flyvbjerg,2 J. L. Andersen,1 P. Aagaard,3 and M. Kjaer1

1Institute of Sports Medicine, Bispebjerg Hospital, and Faculty of Health Sciences, Copenhagen University, Copenhagen; 2Medical Research Laboratories, Clinical Institute and Medical Department M (Diabetes and Endocrinology), Aarhus University Hospital, Aarhus; and 3Institute of Sports Sciences and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark

Submitted 17 April 2008 ; accepted in final form 8 September 2008

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.











Power Output and Muscle Myosin Heavy Chain Composition in Young and Elderly Men.

BASIC SCIENCES
Medicine & Science in Sports & Exercise. 38(9):1601-1607, September 2006.
PEARSON, STEPHEN J. 1,3; COBBOLD, MATTHEW 1; ORRELL, RICHARD W. 2; HARRIDGE, STEPHEN D. R. 1,4

Abstract:
Purpose: Aging is associated with a decline in muscle volume, power output, and the velocity at which peak power (Vopt) occurs. The current study aimed to examine the relationship between lower-limb power output characteristics, muscle myosin heavy chain (MHC) composition, and lean limb volume.

Methods: Lower-limb power output during repeated efforts on an inertial sprint cycle and single-leg thrusts on the modified Nottingham power rig was studied in seven young and seven old males in relation to muscle MHC isoform composition of the vastus lateralis.

Results: Older subjects produced significantly lower power outputs and Vopt under all conditions (P < 0.01) and had lower proportions of fast MHC isoforms (P< 0.05). Peak power output during cycling was significantly related to lower-limb lean volume (r = 0.92, P < 0.05), whereas Vopt during sprint cycling was closely related to vastus lateralis MHC-II composition (r = 0.80, P < 0.05).

Conclusions: These results provide further evidence of the importance of fast myosin isoform composition in the maintenance of dynamic muscle function in later life and particularly for maximal cycling performance.








Exercise Pattern Influences Skeletal Muscle Hybrid Fibers of Runners and Nonrunners.

BASIC SCIENCES
Medicine & Science in Sports & Exercise. 39(11):1977-1984, November 2007.
KOHN, TERTIUS A. 1; ESSEN-GUSTAVSSON, BIRGITTA 2; MYBURGH, KATHRYN H. 1

Abstract:
Purpose: To determine whether relationships between skeletal muscle hybrid fiber composition and whole-body exercise patterns help to elucidate their transitional capacity or a fine-tuning response to functional demands.

Methods: This study investigated hybrid fibers from vastus lateralis biopsies of runners (N= 13) and nonrunners (N = 9) and related hybrid fiber occurrence and distribution of myosin heavy-chain isoforms (MHC) within hybrid fibers to exercise patterns. MHC composition of single fibers was identified by SDS-PAGE.

Results: Runners had more fibers expressing only MHC I, fewer expressing MHC IIx, and fewer IIa/IIx hybrid fibers (P < 0.05). Hybrid IIa/IIx and I/IIa fibers were, respectively, negatively and positively related to training volume or average preferred racing distance (PRDA) in runners (P < 0.05). The relationship between IIa/IIx hybrid fibers and PRDA was more exponential (R2 = 0.88) than linear (R2 = 0.69). Only IIa/IIx hybrid fibers correlated negatively with exercise hours in nonrunners (P < 0.05). Their IIa/IIx hybrid fibers had MHC IIa content ranging from 1 to 99%, with most between 41 and 60%. Runners favoring longer distances (PRDA > 8 km or training > 70 km[middle dot]wk-1) had no IIa/IIx hybrid fibers with MHC IIa proportion > 60%. In these runners, MHC I within hybrid I/IIa fibers was skewed toward higher proportions (> 60%), whereas MHC I proportions were skewed oppositely in runners favoring shorter training or racing distances.

Conclusions: Training volume influences both IIa/IIx and I/IIa hybrid fiber proportions in runners, but only the former in nonrunners. Hybrid IIa/IIx fiber proportions were modulated by racing distance. Distinctly different distributions of MHC isoforms within the hybrid fibers were seen in runners favoring longer distances versus those favoring shorter distances.

adarqui:



Aging, muscle fiber type, and contractile function in sprint-trained athletes
Marko T. Korhonen,1,4 Alexander Cristea,2 Markku Alén,1,4 Keijo Häkkinen,3 Sarianna Sipilä,1,4 Antti Mero,3 Jukka T. Viitasalo,5 Lars Larsson,2,* and Harri Suominen1,4,*

1Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland; 2Department of Clinical Neurophysiology, University of Uppsala, Uppsala, Sweden; 3Department of Biology of Physical Activity, University of Jyväskylä; 4The Finnish Centre for Interdisciplinary Gerontology; 5KIHU — Research Institute for Olympic Sports, Jyväskylä, Finland

Submitted 10 March 2006 ; accepted in final form 9 May 2006

Biopsy samples were taken from the vastus lateralis of 18- to 84-yr-old male sprinters (n = 91). Fiber-type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content were identified using ATPase histochemistry and SDS-PAGE. Specific tension and maximum shortening velocity (Vo) were determined in 144 single skinned fibers from younger (18–33 yr, n = 8) and older (53–77 yr, n = 9) runners. Force-time characteristics of the knee extensors were determined by using isometric contraction. The cross-sectional area of type I fibers was unchanged with age, whereas that of type II fibers was reduced (P < 0.001). With age there was an increased MHC I (P < 0.01) and reduced MHC IIx isoform content (P < 0.05) but no differences in MHC IIa. Specific tension of type I and IIa MHC fibers did not differ between younger and older subjects. Vo of fibers expressing type I MHC was lower (P < 0.05) in older than in younger subjects, but there was no difference in Vo of type IIa MHC fibers. An aging-related decline of maximal isometric force (P < 0.001) and normalized rate of force development (P < 0.05) of knee extensors was observed. Normalized rate of force development was positively associated with MHC II (P < 0.05). The sprint-trained athletes experienced the typical aging-related reduction in the size of fast fibers, a shift toward a slower MHC isoform profile, and a lower Vo of type I MHC fibers, which played a role in the decline in explosive force production. However, the muscle characteristics were preserved at a high level in the oldest runners, underlining the favorable impact of sprint exercise on aging muscle.










Skeletal muscle adaptation: training twice every second day vs. training once daily
Anne K. Hansen, Christian P. Fischer, Peter Plomgaard, Jesper Løvind Andersen, Bengt Saltin, and Bente Klarlund Pedersen

Department of Infectious Diseases and The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark

Submitted 13 February 2004 ; accepted in final form 7 September 2004

Low muscle glycogen content has been demonstrated to enhance transcription of a number of genes involved in training adaptation. These results made us speculate that training at a low muscle glycogen content would enhance training adaptation. We therefore performed a study in which seven healthy untrained men performed knee extensor exercise with one leg trained in a low-glycogen (Low) protocol and the other leg trained at a high-glycogen (High) protocol. Both legs were trained equally regarding workload and training amount. On day 1, both legs (Low and High) were trained for 1 h followed by 2 h of rest at a fasting state, after which one leg (Low) was trained for an additional 1 h. On day 2, only one leg (High) trained for 1 h. Days 1 and 2 were repeated for 10 wk. As an effect of training, the increase in maximal workload was identical for the two legs. However, time until exhaustion at 90% was markedly more increased in the Low leg compared with the High leg. Resting muscle glycogen and the activity of the mitochondrial enzyme 3-hydroxyacyl-CoA dehydrogenase increased with training, but only significantly so in Low, whereas citrate synthase activity increased in both Low and High. There was a more pronounced increase in citrate synthase activity when Low was compared with High. In conclusion, the present study suggests that training twice every second day may be superior to daily training.









Effects of combined strength and sprint training on regulation of muscle contraction at the whole-muscle and single-fibre levels in elite master sprinters
A. Cristea 1,*, M. T. Korhonen 2,3,*, K. Häkkinen 4 , A. Mero 4 , M. Alén 2,3,8,9 , S. Sipilä 2,3 , J. T. Viitasalo 5 , M. J. Koljonen 6 , H. Suominen 2 and L. Larsson 1,7
  1 Department of Clinical Neurophysiology, University of Uppsala, Uppsala, Sweden
  2 Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland
  3 The Finnish Centre for Interdisciplinary Gerontology, Jyväskylä, Finland
  4 Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland
  5 KIHU – Research Institute for Olympic Sports, Jyväskylä, Finland
  6 Kuopio Medical Centre, Kuopio, Finland
  7 Centre for Development and Health Genetics, The Pennsylvania State University, University Park, PA, USA
  8 Department of Medical Rehabilitation, Oulu University Hospital, Oulu, Finland
  9 Institute of Health Sciences, University of Oulu, Oulu, Finland
Correspondence to L. Larsson, Department of Clinical Neurophysiology, Uppsala University, SE-751 85 Uppsala, Sweden. E-mail: lars.larsson@neurofys.uu.se

  *These authors contributed equally to this study.
Copyright Journal compilation © 2008 Scandinavian Physiological Society
KEYWORDS
ageing • fibre types • hypertrophy • master athletes • neural activity • skinned fibres
ABSTRACT

Aim: This study aims at examining the effects of progressive strength and sprint training on regulation of muscle contraction at the whole-muscle and single-fibre levels in older sprint-trained athletes.

Methods: Eleven men (52–78 years) were randomized to a training (EX, n = 7) or control (CTRL, n = 4) group. EX participated in a 20-week programme that combined sprint training with heavy and explosive strength exercises, while CTRL maintained their usual run-based training schedules.

Results: EX improved maximal isometric and dynamic leg strength, explosive jump performance and force production in running. Specific tension and maximum shortening velocity of single fibres from the vastus lateralis were not altered in EX or CTRL. Fibre type and myosin heavy chain isoform distributions remained unchanged in the two groups. There was a general increase in fibre areas in EX, but this was significant only in IIa fibres. The 10% increase in squat jump in EX was accompanied by a 9% increase in the integrated EMG (iEMG) of the leg extensors but the 21–40% increases in isometric and dynamic strength were not paralleled by changes in iEMG.

Conclusion: Adding strength training stimulus to the training programme improved maximal, explosive and sport-specific force production in elite master sprinters. These improvements were primarily related to hypertrophic muscular adaptations.









Effects of power training on muscle structure and neuromuscular performance.

Original Articles
Scandinavian Journal of Medicine & Science in Sports. 15(1):58-64, February 2005.
Kyrolainen, H. 1; Avela, J. 1; McBride, J. M. 2; Koskinen, S. 1; Andersen, J. L. 3; Sipila, S. 4; Takala, T. E. S. 1; Komi, P. V. 1

Abstract:
The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty-three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18 836+/-4282 to 25 443+/-8897 N (P<0.05) during the first 10 weeks of training. In addition, vertical jump height (vertical rise of the center of body mass) in the drop jump test increased significantly (P<0.01). Simultaneously, explosive force production of KE muscles measured as knee moment and power increased significantly; however, there was no significant change (P>0.05) in muscle activity (electromyography) of KE. The mean percentage for myosin heavy chain and titin isoforms, muscle fiber-type distributions and areas were unchanged. The enhanced performance in jumping as a result of power training can be explained, in part, by some modification in the joint control strategy and/or increased RFD capabilities of the KE.

adarqui:
Plasticity of human skeletal muscle: gene expression to in vivo function

Human skeletal muscle is a highly heterogeneous tissue, able to adapt to the different challenges that may be placed upon it. When overloaded, a muscle adapts by increasing its size and strength through satellite-cell-mediated mechanisms, whereby protein synthesis is increased and new nuclei are added to maintain the myonuclear domain. This process is regulated by an array of mechanical, hormonal and nutritional signals. Growth factors, such as insulin-like growth factor I (IGF-I) and testosterone, are potent anabolic agents, whilst myostatin acts as a negative regulator of muscle mass. Insulin-like growth factor I is unique in being able to stimulate both the proliferation and the differentiation of satellite cells and works as part of an important local repair and adaptive mechanism. Speed of movement, as characterized by maximal velocity of shortening (Vmax), is regulated primarily by the isoform of myosin heavy chain (MHC) contained within a muscle fibre. Human fibres can express three MHCs: MHC-I, -IIa and -IIx, in order of increasing Vmax and maximal power output. Training studies suggest that there is a subtle interplay between the MHC-IIa and -IIx isoforms, with the latter being downregulated by activity and upregulated by inactivity. However, switching between the two main isoforms appears to require significant challenges to a muscle. Upregulation of fast gene programs is caused by prolonged disuse, whilst upregulation of slow gene programs appears to require significant and prolonged activity. The potential mechanisms by which alterations in muscle composition are mediated are discussed. The implications in terms of contractile function of altering muscle phenotype are discussed from the single fibre to the whole muscle level.







Changes in muscle force-length properties affect the early rise of force in vivo

Changes in contractile rate of force development (RFD), measured within a short time interval from contraction initiation, were measured after a period of strength training that led to increases in muscle fascicle length but no measurable change in neuromuscular activity. The relationship between training-induced shifts in the moment-angle relation and changes in RFD measured to 30 ms (i.e., early) and 200 ms (i.e., late) from the onset of isometric knee extension force were examined; shifts in the moment-angle relation were used as an overall measure of changes in quadriceps muscle fascicle length. A significant proportion of the variance in RFD measured only in the initial contraction phase (0-30 ms) could be explained by shifts in the moment-angle relation (r = -0.66-0.71; R2 = 0.44-0.50). Training-induced increases in muscle fascicle length may lead to a reduced or complete lack of adaptive gains in contractile RFD, especially in the early contraction phase. Muscle Nerve 39: 512-520, 2009






ADAPTIVE CHANGES OF MYOSIN ISOFORMS IN RESPONSE
TO LONG-TERM STRENGTH AND POWER TRAINING IN
MIDDLE-AGED MEN

The purpose of the study was to examine the adaptive changes in myosin heavy chain (MHC) and light chain
(MLC) isoforms in human vastus lateralis muscle caused by long-term strength and power training (54
weeks, approximately 3 times a week) in untrained middle-aged men (16 in the training and 6 in the control
group). Muscular MHC and MLC isoforms were determined by means of SDS-PAGE gel electrophoresis.
During the training period, maximal anaerobic cycling power increased by 64 W (p < 0.001) and the maximal
jumping height by 1.5 cm (p < 0.05) in the training group, but no significant changes were found in the control
group. However, the group by time effect was not significant. In the training group, the increase of the maximal
jumping height correlated with the number of strength and power training sessions (r = 0.56; p < 0.05). The
change of the proportion of MHC IIa isoform from 52.6 ± 12.2% to 59.4 ± 11.6% did not reach statistical
significance (p = 0.070 for group by time; within training group p = 0.061) and neither did the change of the
proportion of MHC IIx isoform from 18.1 ± 11.4% to 11.1 ± 9.1% (p = 0.104 for group by time; within training
group p=0.032). The degree of change of MHC IIx isoform correlated with the amount of earlier recreational
sports activity (r = 0.61; p < 0.05). In the training group, the changes of MLC1s isoform correlated negatively
with the changes of MLC1f isoform (r = –0.79; p < 0.05) as well as with the changes in maximal anaerobic
cycling power (r = –0.81; p < 0.05), and positively with those of MHC I isoform (r = 0.81; p < 0.05). In
conclusion, the long-term strength and power training 3 times a week seemed to have only slight effects on fast
MHC isoforms in the vastus lateralis muscle of untrained middle-aged men; the proportion of MHC IIa tended to
increase and that of MHC IIx tended to decrease. No changes in MLC isoform profile could be shown







Reduction in hybrid single muscle fiber proportions with resistance training in humans
D. L. Williamson, P. M. Gallagher, C. C. Carroll, U. Raue, and S. W. Trappe

Human Performance Laboratory, Ball State University, Muncie, Indiana 47306

The purpose of this investigation was to examine the effects of 12 wk of progressive resistance training (PRT) on single muscle fiber myosin heavy chain (MHC; I, I/IIa, I/IIa/IIx, IIa, IIa/IIx, IIx) isoform proportions in young individuals. Young, untrained men (YM; n = 6) and women (YW; n = 6) (age = 22 ± 1 and 25 ± 2 yr for YW and YM, respectively) received pre- and post-PRT muscle biopsies from the right vastus lateralis for single muscle fiber MHC distribution by electrophoretic analysis (192 ± 5 pre- and 183 ± 6 post-fibers/subject analyzed; 4,495 fibers total). Data are presented as percentages of the total fibers analyzed per subject. The PRT protocol elicited an increase in the pure MHC IIa (Delta  = + 24 and + 27; YW and YM, respectively; P < 0.05) with no change in the pure MHC I distribution. The hybrid MHC distributions decreased I/IIa/IIx (Delta  = -2; YM and YW; P < 0.05), IIa/IIx (Delta  = -13 and -19 for YM and YW, respectively; P < 0.05), and total hybrid fiber proportion (I/IIa + I/IIa/IIx + IIa/IIx) decreased (Delta  = -19 and -30 for YM and YW, respectively; P < 0.05) with the training, as did the MHC IIx distribution (Delta  = -2; YW only; P < 0.05). Alterations in the predominance of MHC isoforms within hybrid fibers (decrease in MHC I-dominant I/IIa and nondominant MHC IIa/IIx, increase in MHC IIa-dominant IIa/IIx; P < 0.05) appeared to contribute to the increase in the MHC IIa proportion. Electrophoresis of muscle cross sections revealed an ~7% increase (P < 0.05) in MHC IIa proportion in both groups, whereas the MHC IIx decrease by 7.5 and 11.6% post-PRT in YW and YM, respectively. MHC I proportions increase in YM by 4.8% (P < 0.05) post-PRT. These findings further support previous resistance training data in young adults with respect to the increase in the MHC IIa proportions but demonstrate that a majority of the change can be attributed to the decrease in single-fiber hybrid proportions.







Characteristics of myosin profile in human vastus lateralis muscle in relation to training background


Abstract: Twenty-four male volunteers (mean ± SD: age 25.4±5.8 years, height 178.6±5.5 cm, body mass 72.1±7.7 kg) of
different training background were investigated and classified into three groups according to their physical activity and sport
discipline: untrained students (group A), national and sub-national level endurance athletes (group B, 7.8±2.9 years of
specialised training) and sprint-power athletes (group C, 12.8±8.7 years of specialised training). Muscle biopsies of vastus
lateralis were analysed histochemically for mATPase and SDH activities, immunohistochemically for fast and slow myosin,
and electrophoretically followed by Western immunoblotting for myosin heavy chain (MyHC) composition. Significant
differences (P<0.05) regarding composition of muscle fibre types and myosin heavy chains were found only between groups
A (41.7±1.6% of MyHCI, 40.8±4.0% of MyHCIIA and 17.5±4.0% of MyHCIIX) and B (64.3±0.8% of MyHCI, 34.0±1.4%
of MyHCIIA and 1.7±1.4% of MyHCIIX) and groups A and C (59.6±1.6% of MyHCI, 37.2±1.3% of MyHCIIA and 3.2±1.3%
of MyHCIIX). Unexpectedly, endurance athletes (group B) such as long-distance runners, cyclists and cross country skiers,
did not differ from the athletes representing short term, high power output sports (group C) such as ice hockey, karate,
ski-jumping, volleyball, soccer and modern dance. Furthermore, the relative amount of the fastest MyHCIIX isoform in vastus
lateralis muscle was significantly lower in the athletes from group C than in students (group A). We conclude that the myosin
profile in the athletes belonging to group C was unfavourable for their sport disciplines. This could be the reason why those
athletes did not reach international level despite of several years of training







Muscular Performance after Concentric and Eccentric Exercise in Trained Men.

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.






The Role of Dietary Protein Intake and Resistance Training on Myosin Heavy Chain Expression

During resistance training the muscle undergoes many changes. Possibly the most profound and significant changes are those that occur in the muscles contractile proteins. Increases in these contractile proteins are one of the primary factors contributing to myofibrillar hypertrophy. The most abundant muscle protein is myosin, which comprises 25% of the total muscle protein. Due to the large amount of skeletal muscle that is composed of myosin, changes in this fiber may have profound effects on skeletal muscle size and strength. The myosin molecule is made up of 6 subunits, 2 very large heavy chains, and 4 smaller light chains. The myosin heavy chain (MHC) accounts for 25–30% of all muscle proteins making its size an important factor in skeletal muscle growth. In conjunction with resistance training, dietary protein intake must be adequate to illicit positive adaptations. Although many studies have evaluated the role of dietary protein intake on skeletal muscle changes, few have evaluated the MHC specifically. Research has clearly defined the need for dietary protein and resistance training to facilitate positive changes in skeletal muscle. The purpose of this review was to evaluate the current literature on the effects of dietary protein and resistance training on the expression of the myosin heavy chain.

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