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Performance Area => Peer Reviewed Studies Discussion => Topic started by: RJ Nelsen on June 08, 2009, 01:23:51 pm
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All conclusions of studies will be listed in this original post (TABLE OF SUMMARIES) for quick reference.
Post anything related to muscle architecture including what is means, why it's important, the relationship between certain facets of it and performance, and how to affect it via training.
1. Fascicle length of leg muscles is greater in sprinters than distance runners.
Greater fascicle length and lesser pennation angle observed in leg muscles of SPR, compared with DR, would appear to favor shortening velocity as required for greater running speed.
2. Sprint performance is related to muscle fascicle length in male 100-m sprinters.
Muscle thickness was similar between groups for vastus lateralis and gastrocnemius medialis, but S10 had a significantly greater gastrocnemius lateralis muscle thickness. S10 also had a greater muscle thickness in the upper portion of the thigh, which, given similar limb lengths, demonstrates an altered "muscle shape." Pennation angle was always less in S10 than in S11. In all muscles, S10 had significantly greater fascicle length than did S11, which significantly correlated with 100-m best performance (r values from -0.40 to -0.57). It is concluded that longer fascicle length is associated with greater sprinting performance.
3. Effects of physical training and detraining, immobilisation, growth and aging on human fascicle geometry.
ypically, heavy resistance training in young adults has been shown to cause significant increases in fascicle angle of vastus lateralis and triceps brachii as measured by ultrasonography, while high-speed/plyometrics training in the absence of weight training has been associated with increases in fascicle length and a reduction in angles of vastus lateralis fascicles. These changes indicate that differences in geometry between various athletic populations might be at least partly attributable to their differing training regimes.
4. Effects of dynamic resistance training on fascicle length and isometric strength.
At the end of the study, significant increases in vastus lateralis muscle thickness (+6.9%, P < 0.001), fascicle length (+10.3%, P < 0.05), one-repetition maximum (+8.2%, P < 0.05), rate of force development (+23.8%, P < 0.05) and average force produced in the first 500 ms (+11.7%, P < 0.05) were seen only in the training group. Adaptations to the muscle architecture in the training group limited the loss of fibre force, and improved the capacity for developing higher velocities of contraction. The architectural changes in the training group were similar to those seen in studies where high-speed training was performed. In conclusion, dynamic resistance training with light loads leads to increases in muscle thickness and fascicle length, which might be related to a more efficient transmission of fibre force to the tendon.
5. Adaptation to chronic eccentric exercise in humans, the influence of contraction velocity.
After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric [29.6 (6.4)%] and concentric torque [27.4 (7.3)%] at 3.14 rad x s(-1), isometric torque [21.3 (4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad x s(-1). The percentage of type I fibres in the FAST group decreased from [53.8 (6.6)% to 39.1 (4.4)%] while type IIb fibre percentage increased from [5.8 (1.9)% to 12.9 (3.3)%; P < 0.05]. In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque.
6. Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans.
Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training.
7. Electromyostimulation training effects on neural drive and muscle architecture.
At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle.
8. Differential Adaptations to Eccentric versus Conventional Resistance Training in Older Humans.
Training increased fascicle length in both groups, but the increase was significantly greater in the ECC (20% increase) than the CONV (8% increase) group. Conversely, pennation angle significantly increased in the CONV (35%), but not in the ECC (5%) group. Muscle thickness increased to a similar extent in both groups (~12%). In the ECC group, eccentric knee extensor torque increased by 9-17% across velocities, but concentric torque was unchanged. Conversely, in the CONV group, concentric torque increased by 22-37% across velocities, but eccentric torque was unchanged. Instead, isometric torque increased similarly in both groups (~8%). Thus, the two training regimens resulted in differential adaptations in muscle architecture and strength.
9. Effects of eccentric strength training on biceps femoris muscle architecture and knee joint range of movement.
The experimental group completed an eccentric strengthening programme for 8 weeks. Outcome measures included hamstring muscle strength (one repetition maximum), the passive knee extension test (PKE) (knee joint angle at which the onset of passive tension occurs), fascicle length (FL) and pennation angle (PA). One repetition maximum increased by 34% (P < 0.01), the PKE test revealed a 5% increase in joint range of motion (P = 0.01), FL increased by 34% (P = 0.01) and PA did not change (P = 0.38).
10. Differential serial sarcomere number adaptations in knee extensor muscles of rats is contraction type dependent.
Serial sarcomere numbers change differently for the uphill and downhill exercise groups, and for the VL and VI muscles. Short muscle lengths for uphill concentric-biased contractions result in a loss of serial sarcomeres, and long muscle lengths for downhill eccentric-biased contractions result in a gain of serial sarcomeres.
11. Changes in human skeletal muscle induced by long-term eccentric exercise.
Specimens from the controls showed a well-preserved, regular myofibrillar band pattern while changes in the myofibrillar architecture were constantly found in specimens taken after the training program. These changes consisted of Z-band alterations, Z-bands being out of register, extra sarcomeres, Z-band extensions and bisected Z-bands. Between the separated Z-band halves, thin and thick myofilaments as well as abundant glycogen particles and/or ribosomes, were observed. Type-2 (fast-twitch) fibres were predominantly affected. Contrary to the controls the trained individuals constantly showed a greater variation in sarcomere lengths in Type-2 fibres than in Type-1 fibres.
12. Adaptive responses to muscle lengthening and shortening in humans.
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.
13. Myosin heavy chain IIX overshoot in human skeletal muscle
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.
14. Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining
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.
15. Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity
Finally, MHC IIX protein expression was decreased with HL (HEAVY LOAD 70%) but not LL (LIGHT LOAD 15%), 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.
16. Power Output and Muscle Myosin Heavy Chain Composition in Young and Elderly Men.
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).
17. Exercise Pattern Influences Skeletal Muscle Hybrid Fibers of Runners and Nonrunners
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.
18. Aging, muscle fiber type, and contractile function in sprint-trained athletes
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.
19. Skeletal muscle adaptation: training twice every second day vs. training once daily
read the whole study on this one: In conclusion, the present study suggests that training twice every second day may be superior to daily training.
20. Effects of combined strength and sprint training on regulation of muscle contraction at the whole-muscle and single-fibre levels in elite master sprinters
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.
21. Effects of power training on muscle structure and neuromuscular performance.
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.
22. Plasticity of human skeletal muscle: gene expression to in vivo function
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.
23. Changes in muscle force-length properties affect the early rise of force in vivo
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.
24. ADAPTIVE CHANGES OF MYOSIN ISOFORMS IN RESPONSE TO LONG-TERM STRENGTH AND POWER TRAINING IN MIDDLE-AGED MEN
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
25. Characteristics of myosin profile in human vastus lateralis muscle in relation to training background
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
26. Muscular Performance after Concentric and Eccentric Exercise in Trained Men.
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.
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Fascicle length of leg muscles is greater in sprinters than distance runners. (2000).
PURPOSE: The purpose of this study was to compare architectural characteristics of leg muscles of sprinters and distance runners. METHODS: Skeletal muscle architectural characteristics were studied in 23 elite male 100-m sprinters (SPR, 10.0-10.9 s for 100 m), 24 elite male distance runners (DR, 13.5-14.5 min for 5000 m), and 24 untrained male controls. Fascicle pennation angle and isolated muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured in vivo by ultrasound, and fascicle length was estimated. RESULTS: Standing height and upper and lower limb lengths were similar among the groups. Body weight was significantly greater in SPR than in either DR or controls, which were similar. Muscle thickness of the vastus lateralis and gastrocnemius medialis and lateralis muscles was significantly greater in SPR than in either DR or controls, which were similar. In all muscles, pennation angle was similar between SPR and controls, but less than DR. Fascicle length of the vastus lateralis muscle (absolute and relative to limb length) was greatest in SPR and least in DR with control values being between the athlete groups. Fascicle length of the gastrocnemius medialis muscle (absolute and relative to limb length) was greater in SPR than in either DR or controls, which were similar. Fascicle length of the gastrocnemius lateralis muscle (absolute and relative to limb length) was significantly greater in SPR than DR. Absolute fascicle length in gastrocnemius lateralis muscle was similar between DR and controls; however, relative to limb length DR was significantly less. CONCLUSION: Greater fascicle length and lesser pennation angle observed in leg muscles of SPR, compared with DR, would appear to favor shortening velocity as required for greater running speed.
Sprint performance is related to muscle fascicle length in male 100-m sprinters. (2000).
The purpose of this study was to investigate the relationship between muscle fascicle length and sprint running performance in 37 male 100-m sprinters. The sample was divided into two performance groups by the personal-best 100-m time: 10.00-10.90 s (S10; n = 22) and 11.00-11.70 s (S11; n = 15). Muscle thickness and fascicle pennation angle of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Standing height, body weight, and leg length were similar between groups. Muscle thickness was similar between groups for vastus lateralis and gastrocnemius medialis, but S10 had a significantly greater gastrocnemius lateralis muscle thickness. S10 also had a greater muscle thickness in the upper portion of the thigh, which, given similar limb lengths, demonstrates an altered "muscle shape." Pennation angle was always less in S10 than in S11. In all muscles, S10 had significantly greater fascicle length than did S11, which significantly correlated with 100-m best performance (r values from -0.40 to -0.57). It is concluded that longer fascicle length is associated with greater sprinting performance.
Effects of physical training and detraining, immobilisation, growth and aging on human fascicle geometry. (2006).
In addition to its size and the extent of its neural activation, a muscle's geometry (the angles and lengths of its fibres or fascicles) strongly influences its force production characteristics. As with many other tissues within the body, muscle displays significant plasticity in its geometry. This review summarises geometric differences between various athlete populations and describes research examining the plasticity of muscle geometry with physical training, immobilisation/detraining, growth and aging. Typically, heavy resistance training in young adults has been shown to cause significant increases in fascicle angle of vastus lateralis and triceps brachii as measured by ultrasonography, while high-speed/plyometrics training in the absence of weight training has been associated with increases in fascicle length and a reduction in angles of vastus lateralis fascicles. These changes indicate that differences in geometry between various athletic populations might be at least partly attributable to their differing training regimes. Despite some inter-muscular differences, detraining/unloading is associated with decreases in fascicle angle, although little change was shown in muscles such as vastus lateralis and triceps brachii in studies examining the effects of prolonged bed rest. No research has examined the effects of other interventions such as endurance or chronic stretching training. Few data exist describing geometric adaptation during growth and maturation, although increases in gastrocnemius fascicle angle and length seem to occur until maturation in late adolescence. Although some evidence suggests that a decrease in both fascicle angle and length accompanies the normal aging process, there is a paucity of data examining the issue; heavy weight training might attenuate the decline, at least in fascicle length. A significant research effort is required to more fully understand geometric adaptation in response to physical training, immobilisation/detraining, growth and aging.
Effects of dynamic resistance training on fascicle length and isometric strength. (2006).
The aims of this study were to assess changes in muscle architecture, isometric and dynamic strength of the leg extensor muscles, resulting from dynamic resistance training, and the relationships between strength and muscle architecture variables. The participants (n = 30) were randomly assigned to one of two groups. The training group (n = 16; age 21.8 +/- 2.3 years, body mass 74.8 +/- 9.2 kg, height 1.75 +/- 0.08 m) performed dynamic resistance training for 13 weeks. The control group (n = 14; age 19.9 +/- 1.5 years, body mass 74.0 +/- 8.5 kg, height 1.76 +/- 0.05 m) did not perform any resistance training. Maximal dynamic and isometric strength were tested in both groups, before and after the training period. The members of the training group used the free-weight squat lift (90 degrees ) as their training exercise. The concentric phase of the squat was performed explosively. Skeletal muscle architecture of the vastus lateralis was visualized using ultrasonography. At the end of the study, significant increases in vastus lateralis muscle thickness (+6.9%, P < 0.001), fascicle length (+10.3%, P < 0.05), one-repetition maximum (+8.2%, P < 0.05), rate of force development (+23.8%, P < 0.05) and average force produced in the first 500 ms (+11.7%, P < 0.05) were seen only in the training group. Adaptations to the muscle architecture in the training group limited the loss of fibre force, and improved the capacity for developing higher velocities of contraction. The architectural changes in the training group were similar to those seen in studies where high-speed training was performed. In conclusion, dynamic resistance training with light loads leads to increases in muscle thickness and fascicle length, which might be related to a more efficient transmission of fibre force to the tendon.
Adaptation to chronic eccentric exercise in humans: the influence of contraction velocity. (2001).
We compared changes in muscle fibre composition and muscle strength indices following a 10 week isokinetic resistance training programme consisting of fast (3.14 rad x s(-1)) or slow (0.52 rad x s(-1)) velocity eccentric muscle contractions. A group of 20 non-resistance trained subjects were assigned to a FAST (n = 7), SLOW (n = 6) or non-training CONTROL (n = 7) group. A unilateral training protocol targeted the elbow flexor muscle group and consisted of 24 maximal eccentric isokinetic contractions (four sets of six repetitions) performed three times a week for 10 weeks. Muscle biopsy samples were obtained from the belly of the biceps brachii. Isometric torque and concentric and eccentric torque at 0.52 and 3.14 rad x s(-1) were examined at 0, 5 and 10 weeks. After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric [29.6 (6.4)%] and concentric torque [27.4 (7.3)%] at 3.14 rad x s(-1), isometric torque [21.3 (4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad x s(-1). The percentage of type I fibres in the FAST group decreased from [53.8 (6.6)% to 39.1 (4.4)%] while type IIb fibre percentage increased from [5.8 (1.9)% to 12.9 (3.3)%; P < 0.05]. In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque. We conclude that neuromuscular adaptations to eccentric training stimuli may be influenced by differences in the ability to cope with chronic exposure to relatively fast and slow eccentric contraction velocities. Possible mechanisms include greater cumulative damage to contractile tissues or stress induced by slow eccentric muscle contractions.
Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans. (2000).
Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. 2. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. 3. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. 4. Total RNA/wet muscle weight and ty I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72-fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9-fold and 1.2-fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r = 0.66, r = 0.07 and r = -0.71, respectively). 5. The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.
Electromyostimulation training effects on neural drive and muscle architecture. (2005).
PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.
Differential Adaptations to Eccentric versus Conventional Resistance Training in Older Humans. (2009).
We hypothesised that training with eccentric contractions only (therefore utilising higher loads) would yield greater muscle structural and strength gains compared to conventional resistance training. Nine older adults (mean +/- SD age: 74 +/- 3 years) were assigned to a conventional (CONV) resistance training group performing both concentric and eccentric contractions and 10 (age: 67 +/- 2 years) to an eccentric-only (ECC) resistance training group. Both groups trained 3 times per week for 14 weeks at 80% of the 5-repetition maximum, specific to each training mode. Maximum knee extensor torque was assessed during isometric, concentric and eccentric contractions across a range of angular velocities (0-3.49 rad.(-1)). Vastus lateralis muscle architecture (fascicle length, pennation angle and muscle thickness) was assessed in vivo at rest using ultrasonography. Training increased fascicle length in both groups, but the increase was significantly greater in the ECC (20% increase) than the CONV (8% increase) group. Conversely, pennation angle significantly increased in the CONV (35%), but not in the ECC (5%) group. Muscle thickness increased to a similar extent in both groups (~12%). In the ECC group, eccentric knee extensor torque increased by 9-17% across velocities, but concentric torque was unchanged. Conversely, in the CONV group, concentric torque increased by 22-37% across velocities, but eccentric torque was unchanged. Instead, isometric torque increased similarly in both groups (~8%). Thus, the two training regimens resulted in differential adaptations in muscle architecture and strength. These results suggest the stimulus for adding sarcomeres in-series and in-parallel may be different, which implies different myogenic responses induced by the two different training methods.
Effects of eccentric strength training on biceps femoris muscle architecture and knee joint range of movement. (2009).
The aim was to determine whether eccentric strengthening changed the muscle architecture of human biceps femoris and consequently, knee range of motion. Twenty-two subjects were randomly assigned to control and experimental groups. The experimental group completed an eccentric strengthening programme for 8 weeks. Outcome measures included hamstring muscle strength (one repetition maximum), the passive knee extension test (PKE) (knee joint angle at which the onset of passive tension occurs), fascicle length (FL) and pennation angle (PA). One repetition maximum increased by 34% (P < 0.01), the PKE test revealed a 5% increase in joint range of motion (P = 0.01), FL increased by 34% (P = 0.01) and PA did not change (P = 0.38). This is the first report of an increase in FL in the biceps femoris following eccentric resistance training. In addition, the results might imply that this fascicle lengthening could lead to an increase in the range of motion of the knee. Clinical implications for rehabilitation and injury prevention are discussed.
Differential serial sarcomere number adaptations in knee extensor muscles of rats is contraction type dependent. (2005).
Sarcomerogenesis, or the addition of sarcomeres in series within a fiber, has a profound impact on the performance of a muscle by increasing its contractile velocity and power. Sarcomerogenesis may provide a beneficial adaptation to prevent injury when a muscle consistently works at long lengths, accounting for the repeated-bout effect. The association between eccentric exercise, sarcomerogenesis and the repeated-bout effect has been proposed to depend on damage, where regeneration allows sarcomeres to work at shorter lengths for a given muscle-tendon unit length. To gain additional insight into this phenomenon, we measured fiber dynamics directly in the vastus lateralis (VL) muscle of rats during uphill and downhill walking, and we measured serial sarcomere number in the VL and vastus intermedius (VI) after chronic training on either a decline or incline grade. We found that the knee extensor muscles of uphill walking rats undergo repeated active concentric contractions, and therefore they suffer no contraction-induced injury. Conversely, the knee extensor muscles during downhill walking undergo repeated active eccentric contractions. Serial sarcomere numbers change differently for the uphill and downhill exercise groups, and for the VL and VI muscles. Short muscle lengths for uphill concentric-biased contractions result in a loss of serial sarcomeres, and long muscle lengths for downhill eccentric-biased contractions result in a gain of serial sarcomeres.
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awesome.. great studies
these studies really apply to what I am currently doing from jun-aug... so it should be very interesting to see how all of this will apply.
peace & thanks man good stuff.
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Changes in human skeletal muscle induced by long-term eccentric exercise. (1984).
The fine structure of muscle fibres from m. vastus lateralis of nine healthy males (mean age 26 years) was investigated. Four individuals constituted non-exercised controls while five subjects participated in a two-months eccentric muscular training program. Specimens from the controls showed a well-preserved, regular myofibrillar band pattern while changes in the myofibrillar architecture were constantly found in specimens taken after the training program. These changes consisted of Z-band alterations, Z-bands being out of register, extra sarcomeres, Z-band extensions and bisected Z-bands. Between the separated Z-band halves, thin and thick myofilaments as well as abundant glycogen particles and/or ribosomes, were observed. Type-2 (fast-twitch) fibres were predominantly affected. Contrary to the controls the trained individuals constantly showed a greater variation in sarcomere lengths in Type-2 fibres than in Type-1 fibres. It is concluded that muscular work of high tension can induce fine-structural alterations. When repeated over a long period of time, extreme tension demands seem to initiate reorganization in the muscle fibres, predominantly in the, ultrastructurally defined, Type-2 fibres. This adaptation probably results in a better stretchability of the muscle fibres, reduces the risk for mechanical damage and brings about an optimal overlap between actin and myosin filaments.
Adaptive responses to muscle lengthening and shortening in humans. (1996).
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.
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study 12 is very nice.. never seen that one.
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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.
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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.
nice..
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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.
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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.
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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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I wonder what RJ is up to nowadays