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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.
... We have previously observed slowing of evoked contractile properties following longitudinal RT 10 and in long-term resistance trained (≥3 years) compared to untrained individuals. 55 The slowing of evoked muscle contractile properties is likely due to decreased expression of myosin heavy-chain type IIX fibers after RT. 56,57 Therefore, the tendency for less slowing of the muscle after CP supplementation could conceivably indicate type IIX fiber retention or greater type II muscle fiber hypertrophy in this group although greater type II fiber hypertrophy was not observed in a prior study that combined RT and CP supplementation. 38 ...
... Using detailed analysis of explosive torque at multiple time points, we found 15 weeks of RT only enhanced the late phase of explosive contraction (150 ms) for PLA, and the middle and late phases (100 and 150 ms) for CP, with no changes in the early phase of contraction (50 ms) for either group. The finding that conventional heavy, slow RT (i.e., not specifically explosive) does not enhance early phase explosive strength/rate of force development is in accordance with previous isometric 10, 57 and dynamic 63,64 RT studies. Relative explosive strength (i.e., relative to MVT) decreased in both CP and PLA groups with no betweengroup differences detected. ...
... The load for each exercise was increased if the participant could do all the specified repetitions on the penultimate set of an exercise, a common approach to achieve progressive overload. 57,[63][64][65] Bilateral warm-up sets were completed before the unilateral knee extension and bilateral knee flexion exercises with the same number of repetitions and with ~50% of the load to be lifted in the first main set. ...
Aim:
Bioactive collagen peptides (CP) have been suggested to augment the functional, structural (size and architecture) and contractile adaptations of skeletal muscle to resistance training (RT), but with limited evidence. This study aimed to determine if CP vs placebo (PLA) supplementation enhanced the functional and underpinning structural, and contractile adaptations after 15 weeks of lower body RT.
Methods:
Young healthy males were randomized to consume either 15 g of CP (n=19) or PLA (n=20) once every day during a standardized program of progressive knee extensor, knee flexor and hip extensor RT 3 times/wk. Measurements pre and post RT included: knee extensor and flexor isometric strength; quadriceps, hamstrings and gluteus maximus volume with MRI; evoked twitch contractions, 1RM lifting strength and architecture (with ultrasound) of the quadriceps.
Results:
Percentage changes in maximum strength (isometric or 1RM) did not differ between groups (0.684≤P≤0.929). Increases in muscle volume were greater (quadriceps 15.2 vs. 10.3%; vastus medialis (VM) 15.6 vs. 9.7%; total muscle volume 15.7 vs. 11.4%; [all] P≤0.032) or tended to be greater (hamstring 16.4 vs. 12.5%; gluteus maximus 16.6 vs. 12.9%; 0.089≤P≤0.091) for CP vs. PLA. There were also greater increases in twitch peak torque (22.3 vs. 12.3%; P=0.038) and angle of pennation of the VM (16.8 vs. 5.8%, P=0.046), but not other muscles, for CP vs. PLA.
Conclusions:
CP supplementation produced a cluster of consistent effects indicating greater skeletal muscle remodelling with RT compared to PLA. Notably, CP supplementation amplified the quadriceps and total muscle volume increases induced by RT.
... Regardless of the amount of muscle mass existing in a thrower's body, this muscle mass must be activated in order to produce power. Accordingly, it is assumed that the recruitment of a large number of muscle fibers, especially type II muscle fibers, is necessary for high power outputs [53,54]. Muscle fiber recruitment during high-velocity movements is difficult to measure; therefore, researchers have attempted to evaluate the activation of muscles with surface electromyography (EMG). ...
... There seems to be a consensus that fiber type composition and cross-sectional area (CSA) determine a large part of the muscle power capacity [53,[55][56][57]. Three types of fibers have been identified in human skeletal muscles: type I, IIA and IIX, with type I having the lowest and type IIX the highest shortening velocities (Figure 2) [58]. ...
... Muscle fiber type composition is thought to be determined mainly by hereditary factors [61], although this still remains debated. Nevertheless, a common finding is that resistance training induces a transformation of type IIX to IIA muscle fibers, while detraining leads to the opposite fiber type transformation [53,55]. This phenomenon might be of great importance when preparing for a track and field throwing competition. ...
Track and field throwing performance is determined by a number of biomechanical and biological factors which are affected by long-term training. Although much of the research has focused on the role of biomechanical factors on track and field throwing performance, only a small body of scientific literature has focused on the connection of biological factors with competitive track and field throwing performance. The aim of this review was to accumulate and present the current literature connecting the performance in track and field throwing events with specific biological factors, including the anthropometric characteristics, the body composition, the neural activation, the fiber type composition and the muscle architecture characteristics. While there is little published information to develop statistical results, the results from the current review suggest that major biological determinants of track and field throwing performance are the size of lean body mass, the neural activation of the protagonist muscles during the throw and the percentage of type II muscle fiber cross-sectional area. Long-term training may enhance these biological factors and possibly lead to a higher track and field throwing performance. Consequently, coaches and athletes should aim at monitoring and enhancing these parameters in order to increase track and field throwing performance.
... One possible mechanism which may also contribute to the increase in power development during a taper is a shift in myosin heavy chain (MHC) isoform. Several studies have cited a shift from slower to faster isoforms during periods of reduced training [35][36][37]. Andersen et al. (2000) studied changes in MHC after three months of heavy resistance training and again after three months of detraining [35]. The results showed a significant shift of type IIx MHC to MHC IIa after resistance training with significant hypertrophy of the type II fibers. ...
... Several studies have cited a shift from slower to faster isoforms during periods of reduced training [35][36][37]. Andersen et al. (2000) studied changes in MHC after three months of heavy resistance training and again after three months of detraining [35]. The results showed a significant shift of type IIx MHC to MHC IIa after resistance training with significant hypertrophy of the type II fibers. ...
... Several studies have cited a shift from slower to faster isoforms during periods of reduced training [35][36][37]. Andersen et al. (2000) studied changes in MHC after three months of heavy resistance training and again after three months of detraining [35]. The results showed a significant shift of type IIx MHC to MHC IIa after resistance training with significant hypertrophy of the type II fibers. ...
Some controversy exists as to the most efficacious method of training to achieve enhanced levels of sport performance. Controversy concerning the efficacy of periodization and especially block periodization (BP) likely stems from the use of poorly or untrained subjects versus trained who may differ in their responses to a stimulus. The purpose of this study was to investigate the effect of training status on performance outcomes resulting from 11 weeks of BP training. Fifteen males were recruited for this study and placed into strong (age = 24.3 ± 1.9 years., body mass (BM) = 87.7 ± 8.7 kg, squat: body mass = 1.96 ± 0.16), moderate (age = 25.3 ± 2.7 years., body mass = 100.2 ± 15.5 kg, squat: body mass = 1.46 ± 0.14), or weak (age = 23.2 ± 3.9 yrs., body mass = 83.5 ± 17.1 kg, squat: body mass = 1.17 ± 0.07) groups based on relative strength. Testing was completed at baseline, and after each block which consisted of 1 repetition maximum (1RM) squat, 0 kg static jump (SJ), 0 kg countermovement jump (CMJ), 20 kg SJ, and 20 kg CMJ. Absolute and relative strength were strongly correlated with rates of improvement for absolute strength, relative strength, 0 kg, and 20 kg vertical jumps. All subjects substantially improved back squat (p < 0.001), relative back squat (p < 0.001) with large-very large effect sizes between groups for percent change favoring the weak group over the moderate and strong group for all performance variables. All subjects showed statistically significant improvements in 0 kg SJ (p < 0.001), 0 kg CMJ (p < 0.001), 20 kg SJ (p = 0.002), and 20 kg CMJ (p < 0.001). Statistically significant between group differences were noted for both 20 kg SJ (p = 0.01) and 20 kg CMJ (p = 0.043) with the strong group statistically greater jump heights than the weak group. The results of this study indicate BP training is effective in improving strength and explosive ability. Additionally, training status may substantially alter the response to a resistance training program.
... Myoplasticity has been defined as the capacity of skeletal muscle to alter its structural and enzymatic protein content according to changes in use and the environment (i.e., the training stressor); the effects are predominantly a result of changes in gene expression [147]. It is evident that regardless of training for hypertrophy or strength, if the training volume is increased enough and the intensity is prescribed appropriately, the physiological response may result in hypertrophic adaptations associated with fiber type mutations [148][149][150]. Skeletal muscle in humans is predominately characterized based on MHC isoforms, as previously discussed, categorized as type I, II, and IIX, along with intermediate hybrid muscle fibers such as I/IIA, IIA/IIX, and I/IIA/IIX, with each displaying specific and unique morphological, biochemical, metabolic, and contractile proprieties [151][152][153][154][155]. Regardless of pure or hybrid isoforms, type II fiber content appears to influence whole muscle function, and often correlates strongly with athletic performance associated with force, velocity, and power production [134,140,142,143,151]. ...
... Skeletal muscle in humans is predominately characterized based on MHC isoforms, as previously discussed, categorized as type I, II, and IIX, along with intermediate hybrid muscle fibers such as I/IIA, IIA/IIX, and I/IIA/IIX, with each displaying specific and unique morphological, biochemical, metabolic, and contractile proprieties [151][152][153][154][155]. Regardless of pure or hybrid isoforms, type II fiber content appears to influence whole muscle function, and often correlates strongly with athletic performance associated with force, velocity, and power production [134,140,142,143,151]. The genetic machinery of each fiber type responds to training stimuli by releasing specific mRNA proteins and changing the anatomical mCSA and fCSA, where fibers can take on characteristics of other fiber types (e.g., shifting from MHC-I→MHC-IIA; MHC-IIA/IIX→MHC-IIA) by adapting to the given stressor [87,149,150,156]. However, while fiber shifts may have been observed from type II to I [157], fibers appear to be capable of shifting across the fiber type spectrum predominately taking place within type II fiber content (e.g., IIA→ IIX; IIX→IIA) [155,156,[158][159][160]. ...
... For each fiber type, a cross-bridge is the single force generating unit that interacts with thin filaments pulling towards the center of the sarcomere interrelating with specific isoforms which can be altered further through specific training emphasis [221]. Although other proteins and contractile systems are involved with fine-tuning contraction, the prime determinant of force generation is the MHC isoform [222], which is influenced by the training mode [149,223]. Due to biochemical limitations of cross-bridge dissociation, there is a limit on how fast a fiber, and therefore, a whole muscle, is able to contract [224]. There are several muscular structural adaptations that take place due to strength training after task-specific hypertrophy is achieved that aid further in the mechanisms associated with strength changes. ...
While strength is indeed a skill, most discussions have primarily considered structural adaptations rather than ultrastructural augmentation to improve performance. Altering the structural component of the muscle is often the aim of hypertrophic training, yet not all hypertrophy is equal; such alterations are dependent upon how the muscle adapts to the training stimuli and overall training stress. When comparing bodybuilders to strength and power athletes such as powerlifters, weightlifters, and throwers, while muscle size may be similar, the ability to produce force and power is often inequivalent. Thus, performance differences go beyond structural changes and may be due to the muscle's ultrastructural constituents and training induced adaptations. Relative to potentiating strength and power performances, eliciting specific ultrastructural changes should be a variable of interest during hypertrophic training phases. By focusing on task-specific hypertrophy, it may be possible to achieve an optimal amount of hypertrophy while deemphasizing metabolic and aerobic components that are often associated with high-volume training. Therefore, the purpose of this article is to briefly address different types of hypertrophy and provide directions for practitioners who are aiming to achieve optimal rather than maximal hypertrophy, as it relates to altering ultrastructural muscular components, to potentiate strength and power performance.
... In adult human skeletal muscle, three different muscle fiber types (i.e., type I, type IIa and type IIx) are distinguished which are characterized by the myosin heavy chain isoform that is expressed (Myh7, Myh2 or Myh1) [7]. Interestingly, type I fibers are relatively small with a high oxidative-but also a higher protein synthesis capacity than type II fibers [8], while intriguingly type II fibers show more hypertrophy than type I fibers after resistance exercise [9,10]. Because type II fibers rely more on glycolysis for energy production than type I fibers [7], there might be a yet an unknown role of glycolysis in skeletal muscle hypertrophy that could explain the distinct growth responses seen in type I and type II fibers. ...
... Notably, PKM2 was higher following the 10-day rest period (T14) compared to levels after 13 training sessions ( Figure 2D). A detraining phase following resistance exercise can increase the number of type IIx fibers, creating a more glycolytic muscle [9,38]. Perhaps this could explain the increase in PKM2 abundance after the rest period. ...
... Prior to the study, subjects were tested for 10 repetitions maximum (10 RM) on a dual-legged knee-extension and leg press machine (Gym 80, Gelsenkirchen, Germany), where the training sessions were carried out. For all further training sessions (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), subjects performed three sets ranging between eight and twelve repetitions of leg extensions followed by leg press exercises. The movement speed consisted of 2 s concentric, 1 s isometric and 2 s eccentric movement with an 80 degree range of motion. ...
Nearly 100 years ago, Otto Warburg investigated the metabolism of growing tissues and discovered that tumors reprogram their metabolism. It is poorly understood whether and how hypertrophying muscle, another growing tissue, reprograms its metabolism too. Here, we studied pyruvate kinase muscle (PKM), which can be spliced into two isoforms (PKM1, PKM2). This is of interest, because PKM2 redirects glycolytic flux towards biosynthetic pathways, which might contribute to muscle hypertrophy too. We first investigated whether resistance exercise changes PKM isoform expression in growing human skeletal muscle and found that PKM2 abundance increases after six weeks of resistance training, whereas PKM1 decreases. Second, we determined that Pkm2 expression is higher in fast compared to slow fiber types in rat skeletal muscle. Third, by inducing hypertrophy in differentiated C2C12 cells and by selectively silencing Pkm1 and/or Pkm2 with siRNA, we found that PKM2 limits myotube growth. We conclude that PKM2 contributes to hypertrophy in C2C12 myotubes and indicates a changed metabolic environment within hypertrophying human skeletal muscle fibers. PKM2 is preferentially expressed in fast muscle fibers and may partly contribute to the increased potential for hypertrophy in fast fibers.
... 7 The question of whether muscle fiber types can change phenotype from one type to another as a result of changes in muscle activity has been studied experimentally since the start of the 1960s and 1970s in animal models 8 and humans, 9 respectively. In humans, the type 2A and type 2X muscle fibers seem to readily interconvert in response to changes in physical activity patterns, in that increased physical activity increases the relative number of type 2A muscle fibers on the expense of the relative number of type 2X muscle fibers, [10][11][12] and vice versa by reduced activity patterns. 11,12 However, it is unclear whether this fiber type plasticity also extends to the type 1 fibers in humans. ...
... In humans, the type 2A and type 2X muscle fibers seem to readily interconvert in response to changes in physical activity patterns, in that increased physical activity increases the relative number of type 2A muscle fibers on the expense of the relative number of type 2X muscle fibers, [10][11][12] and vice versa by reduced activity patterns. 11,12 However, it is unclear whether this fiber type plasticity also extends to the type 1 fibers in humans. In physiologically intact rodents, models of reduced muscle activity induce a pattern of fiber type transformation going from the "slow" to the "fast" fiber types, that is a reduction of the proportion of type 1 fibers and a concomitant increase in the relative proportion of the fastest fiber types. ...
... 13,14 This observation indicates that prolonged reductions in-or loss of voluntary muscle activation can convert the type 1 fibers to type 2 fibers. However, in studies of persons with intact nerve supply, decreased physical activity patterns such as detraining and immobilization have reported both reductions, 15,16 increases 17 and no change 11,12 in the type 1 muscle fiber proportion. Presently, it seems uncertain whether changes in the muscle fiber type 1 proportions occur in response to patterns of reduced physical activity under normal physiological conditions. ...
The main objective of this systematic review was to examine the effect of reduced muscle activity on the relative number of type 1 muscle fibers (%) in the human vastus lateralis muscle. Other objectives were changes in type 2A and 2X percentages and muscle fiber cross‐sectional area. We conducted systematic literature searches in eight databases and included studies assessing type 1 fiber percentage visualized by ATPase‐ or immunohistochemical staining before‐ and after a period (≥ 14 days) of reduced muscle activity. The reduced muscle activity models were detraining, leg unloading and bed rest. Forty‐two studies comprising 451 participants were included. Effect sizes were calculated as the mean difference between baseline and follow‐up and Generic Inverse Variance tests with random effects models was used for the weighted summary effect size. Overall, the mean type 1 muscle fiber percentage was significantly reduced after interventions (‐1.94 %‐points, 95 % CI [‐3.37, ‐0.51], p = 0.008), with no significant differences between intervention models (p = 0.86). Meta‐regression showed no effect of study duration on type 1 fiber percentage (p = 0.98). Conversely, the overall type 2X fiber percentage increased after reduced muscle activity (p < 0.001). The CSA of the muscle fiber types decreased after the study period (all p‐values < 0.001) with greater reductions in type 2 than type 1 fibers (p < 0.001). The result of this meta‐analysis display that the type 1 muscle fiber percentage decrease as a result of reduced muscle activity, although the effect size is relatively small.
... Muscle fiber-type proportion is another major factor in RTD performance, with explosive training-induced fiber type shifts linked to changes in early-phase RTD (12). While fiber type proportion has a genetic predisposition (30), a high degree of adaptability in the myosin heavy chain isoform used to classify fiber types has been observed (31). Previous comparisons of the fiber type proportion of fast-twitch fibers of the lateral gastrocnemius (32) identified a larger proportion of type II fast-twitch fibers in sprinters (~73-76 %) compared to endurance athletes (~39-48%) and untrained participants (~47-49%). ...
... This is similar to previous research reporting similar tendon stiffness between sprinters and untrained participants (37). Fiber type proportion differences, which are adaptable to training type (31,39) may account for the EMD differences between the groups. However, these were not examined in the current study. ...
ABSTRACT
Introduction: Comparison of the neuromuscular performance of different athlete types may give insight into the in-vivo variability of these measures and their underpinning mechanisms. The study aims to compare the neuromuscular function of the plantar flexors of sprinters and physically active individuals to assess any differences in explosive force performance. Methods: Neuromuscular performance of a group of sprinters (highly trained/national level, n = 12; elite/international level, n = 2) and physically active individuals (n = 14) were assessed during involuntary, explosive, and maximum voluntary isometric plantar flexions, across different muscle-tendon unit (MTU) lengths (10° plantarflexion (PF), 0° (anatomical zero/neutral, AZ), and 10° dorsiflexion (DF)). Plantarflexion rate of torque development (RTD) was measured in three 50-ms time windows from their onset. The synchronous activation of the plantar flexor agonist muscles was calculated as the time difference between 1) the first and last muscle onset and 2) the onsets of the two gastrocnemii muscles. Muscle size and MTU stiffness were assessed using sonograms of the medial gastrocnemius and myotendinous junction. Results: Sprinters exhibited greater involuntary RTD across time points (0-50, 50-100 ms) and MTU lengths. Additionally, sprinters demonstrated greater early phase voluntary RTD (0-50, 50-100 ms) across MTU lengths. Sprinters also demonstrated greater late-phase RTD (100-150 ms), and relative maximal voluntary torque at the DF angle only. The sprinters demonstrated a more synchronous activation of the gastrocnemii muscles. There were no observable differences in muscle size and MTU stiffness between groups. Conclusions: These findings suggest sprint-specific training could be a contributing factor toward improved explosive performance of the plantar flexors, particularly in the early phase of muscular contraction, evidenced by the greater explosive torque producing capabilities of sprinters.
... Shifting between fast twitch sub-fibre types (i.e. MyHC IIa ↔ IIx) can occur Table 1 The effects of various training methods on the determinants of maximal muscular power, sustained power production during brief maximal efforts, and rates of recovery in response to training and detraining [138][139][140][141][142], but it is less clear if shifts between type I and type II fibres occur in humans [79,[143][144][145]. Sprint training does seem to induce a bidirectional shift (i.e. ...
... MyHC I → IIa ← IIx) with the slowest and fastest MyHC isoforms converging towards an intermediate isoform [146][147][148]. A period of detraining following resistance training may also induce an 'overshoot' of MyHC IIx composition above pre-training levels, largely at the expense of MyHC IIa fibres [141,146], which has been associated with an increased maximal shortening velocity and highvelocity force production [149]. However, the detrimental effects of detraining on maximal force, power and fatigue-resistance [149][150][151], could possibly outweigh the positive effects of improved high-velocity contractile performance in trained sprint cyclists. ...
Maximal muscular power production is of fundamental importance to human functional capacity and feats of performance. Here, we present a synthesis of literature pertaining to physiological systems that limit maximal muscular power during cyclic actions characteristic of locomotor behaviours, and how they adapt to training. Maximal, cyclic muscular power is known to be the main determinant of sprint cycling performance, and therefore we present this synthesis in the context of sprint cycling. Cyclical power is interactively constrained by force-velocity properties (i.e. maximum force and maximum shortening velocity), activation-relaxation kinetics and muscle coordination across the continuum of cycle frequencies, with the relative influence of each factor being frequency dependent. Muscle cross-sectional area and fibre composition appear to be the most prominent properties influencing maximal muscular power and the power-frequency relationship. Due to the role of muscle fibre composition in determining maximum shortening velocity and activation-relaxation kinetics, it remains unclear how improvable these properties are with training. Increases in maximal muscular power may therefore arise primarily from improvements in maximum force production and neuromuscular coordination via appropriate training. Because maximal efforts may need to be sustained for~15-60 s within sprint cycling competition, the ability to attenuate fatigue-related power loss is also critical to performance. Within this context, the fatigued state is characterised by impairments in force-velocity properties and activation-relaxation kinetics. A suppression and leftward shift of the power-frequency relationship is subsequently observed. It is not clear if rates of power loss can be improved with training, even in the presence adaptations associated with fatigue-resistance. Increasing maximum power may be most efficacious for improving sustained power during brief maximal efforts, although the inclusion of sprint interval training likely remains beneficial. Therefore, evidence from sprint cycling indicates that brief maximal muscular power production under cyclical conditions can be readily improved via appropriate training, with direct implications for sprint cycling as well as other athletic and health-related pursuits. Maximal muscle power production under cyclical conditions is interactively constrained by force-velocity properties, activation-relaxation kinetics and muscle coordination across the continuum of possible movement frequencies. Fatigue alters the power-frequency relationship, with a higher degree of power loss at higher movement frequencies. Maximal muscular power production can be readily increased with appropriate strength and power training; it remains less clear if rates of power loss during brief maximal sustained efforts can be improved with training.
... Muscle biopsies (vastus lateralis) were obtained pre-and post-intervention for male participants only, as described in details elsewhere [31][32][33]. Briefly, muscle samples were mounted with Tissue-Tek (4583, Sakura Finetek Europe B. V., Alphen aan den Rijn, Holland) and immediately frozen in isopentane cooled with liquid nitrogen and stored at -80˚C until later histochemical analysis. ...
... Briefly, muscle samples were mounted with Tissue-Tek (4583, Sakura Finetek Europe B. V., Alphen aan den Rijn, Holland) and immediately frozen in isopentane cooled with liquid nitrogen and stored at -80˚C until later histochemical analysis. Serial sections (10μm) were cut in a cryostat (-20˚C, Cyros ARNX70, Thermo Scientific, Walldorf, Germany) and ATPase staining with preincubation at pH 4.37, 4.54, and 10.30 were performed [31,34]. In addition, immunohistochemistry staining of capillaries was performed using the double staining method [35]. ...
Prolonged physical inactivity in young adults may lead to deficiencies in musculoskeletal fitness, and thus a need exists to develop physical activity and exercise programmes that are effective of increasing musculoskeletal fitness. The aim of this study, therefore, was to investigate the effects of small-sided team handball training on lower limb muscle strength, postural balance and body composition in young adults. Twenty-six men and twenty-eight women were stratified for peak oxygen uptake (VO2peak) and body fat percentage and randomly allocated to either 12 wks of small-sided recreational team handball training (THG: 14 men and 14 women, age 24.1±2.6 yrs (mean±SD), VO2peak 39.8±5.9 ml/kg/min and body fat percentage 32.7±8.7%) or serving as non-exercising controls (CON: 12 men and 14 women, age 24.8±3.1 yrs, VO2peak 39.7±5.0 ml/kg/min, body fat percentage 31.7±9.7%). THG trained on average 1.8 times/week for 12 wks. At 0 and 12 wks, lower limb muscle strength, rate of force development (RFD), vertical jump height and power, postural balance, body composition and muscle biopsies were assessed. No training effects were observed for maximal isokinetic or isometric knee extensor strength, maximal vertical jump height or take-off power, fibre type distribution or capillarization. Late phase (RFD) increased (+7.4%, p
... 22 This was followed by rinse in 1% CaCl 2 for 1, 2 and 3 min and incubation in a 2% CoCl 2 solution for 3 min. The slides were washed 25 times in H 2 O and incubated with 1% ammoniumsulfide for 1 min, then washed again 25 times in H 2 O and mounted with polyvinylpyrrolidon. 23 Furthermore, a double staining method combining ulex europaeus lectin 1 (UEA-1) and collagen type IV staining was used for immunohistochemistry staining of muscle fiber membranes as described in details elsewhere. 24 A Olympus BX40 microscope (Olympus Optical Co., Tokyo, Japan), connected to a Sanyo Hi-resolution Color CCD camera (Sanyo Electronic Co., Osaka, Japan), an eight-bit Matrox Meteor Framegrabber (Matrox Electronic Systems, Quebec, Canada), and image-analysis software (Tema, Scanbeam, Hadsund, Denmark) allowed identification of fiber types, size and membrane. ...
... The relative proportion of five different fiber types (types I, I/IIa, IIa, IIax, and IIx) were determined including their size. 23 Calculations of fiber size were performed only for fiber types I and II. On average, 116 ± 40 (n = 24) fibers were used for determining fiber size and 134 ± 25 (n = 35) for fiber type in each biopsy. ...
Objectives
Military-, rescue- and law-enforcement personnel require a high physical capacity including muscular strength. The present study hypothesized that 9 weeks of volume matched concurrent short frequent training sessions increases strength more efficiently than less frequent longer training sessions.
Design
A randomized training intervention study with functional and physiological tests before and after the intervention.
Method
Military conscripts (n = 290) were assigned to ‘micro-training’ (MIC: four 15-min strength and four 15-min endurance bouts weekly); ‘classical-training’ (CLA: one 60-min strength and one 60-min endurance training session weekly) or a ‘control-group’ (CON: two 60-min standard military physical training sessions weekly).
Results
There were no group difference between MIC and CLA in measures of strength. Standing long jump remained similar while shotput performance was reduced (P ≤ 0.001) in all three groups. Pull-up performance increased (P ≤ 0.001) in MIC (7.4 ± 4.6 vs. 8.5 ± 4.0 repetitions, n = 59) and CLA (5.7 ± 4.1 vs. 7.1 ± 4.2 repetitions, n = 50). Knee extensor MVC increased (P ≤ 0.01) in all groups (MIC, n = 30, 11.5 ± 8.9%; CLA, n = 24, 8.3 ± 11.5% and CON, n = 19, 7.5 ± 11.8%) while elbow flexor and hand grip MVC remained similar. MIC increased (P ≤ 0.05) type IIa percentage from 32.5 ± 11.0% to 37.6 ± 12.3% (n = 20) and CON increased (P ≤ 0.01) type IIax from 4.4 ± 3.0% to 11.6 ± 7.9% (n = 8). In CON type I, fiber size increased (P ≤ 0.05) from 5121 ± 959 μm to 6481 ± 2084 μm (n = 5). Satellite cell content remained similar in all groups.
Conclusion
Weekly distribution of low-volume concurrent training completed as either eight 15-min bouts or two 60-min sessions of which 50% was strength training did not impact strength gains in a real-world setting.
... The greater effect of multiple-set training coincided with greater responses in muscle biological traits indicative of hypertrophic response (Andersen & Aagaard, 2000;Goodman et al., 2011;Terzis et al., 2008;Luo et al., 2019;Stec et al., 2016), including greater transition from Type IIX to IIA muscle fibres, greater post-exercise phosphorylation S6K1 and ribosomal protein S6, greater post-exercise expression of c-Myc and greater rested-state levels of total RNA and ribosomal RNA. While most of these variables are already assumed to be volume sensitive, such as muscle mass and strength (Krieger, 2009(Krieger, , 2010Schoenfeld et al., 2016) and mTOR-signalling (Burd et al., 2010;Terzis et al., 2010), this is the first study to suggest that the IIX IIA fiber switch is also volume sensitive. ...
... Importantly, this adaptation is a hallmark of resistance training adaptations (Andersen & Aagaard, 2000). This study also suggests that the volume-sensitive increase in ribosomal content is essential for beneficial effects of increases in training volume on muscle growth and strength, as shown by thirteen and sixteen of the participants respectively. ...
Key points:
For individuals showing suboptimal adaptations to resistance training, manipulation of training volume is a potential measure to facilitate responses. This remains unexplored. Here, 34 untrained individuals performed contralateral resistance training with moderate and low volume for 12 weeks. Moderate volume led to larger increases in muscle cross-sectional area, strength and type II fibre-type transitions. These changes coincided with greater activation of signalling pathways controlling muscle growth and greater induction of ribosome synthesis. Thirteen and sixteen participants, respectively, displayed clear benefits of moderate-volume training on muscle hypertrophy and strength. This coincided with greater total RNA accumulation in the early-phase of the training period, suggesting that ribosomal biogenesis regulates the dose-response relationship between training volume and muscle hypertrophy. These results demonstrate that there is a dose-dependent relationship between training volume and outcomes. On the individual level, benefits of higher training volume were associated with increased ribosomal biogenesis.
Abstract:
Resistance-exercise volume is a determinant of training outcomes. However not all individuals respond in a dose-dependent fashion. In this study, 34 healthy individuals (males n = 16, 23.6 (4.1) years; females n = 18, 22.0 (1.3)) performed moderate- (3 sets per exercise, MOD) and low-volume (1 set, LOW) resistance training in a contralateral fashion for 12 weeks (2-3 sessions × week-1 ). Muscle cross-sectional area (CSA) and strength were assessed at weeks 0 and 12, along with biopsy sampling (m. Vastus lateralis). Muscle biopsies were also sampled before and one hour after the fifth session (Week 2). MOD resulted in larger increases in muscle CSA (5.2 (3.8)% versus 3.7 (3.7)%, P < 0.001) and strength (3.4-7.7% difference, all P < 0.05. This coincided with greater reductions in type IIX fibres from week 0 to 12 (MOD, -4.6; LOW -3.2%-point), greater phosphorylation of S6-kinase 1 (p85 S6K1Thr412 , 19%; p70 S6K1Thr389 , 58%) and ribosomal protein S6Ser235/236 (37%), greater rested-state total RNA (8.8%) and greater exercise-induced c-Myc mRNA expression (25%; Week 2, all P < 0.05). Thirteen and sixteen participants, respectively, displayed clear benefits in response to MOD on muscle hypertrophy and strength. Benefits were associated with greater accumulation of total RNA at Week 2 in the MOD leg, with every 1% difference increasing the odds of MOD benefit by 7.0% (P = 0.005) and 9.8% (P = 0.002). In conclusion, MOD led to greater functional and biological adaptations than LOW. Associations between dose-dependent total RNA accumulation and increases in muscle mass and strength points to ribosome biogenesis as a determinant of dose-dependent training responses. This article is protected by copyright. All rights reserved.
... A literatura científica tem demonstrado que, de maneira crônica, determinados protocolos de treinamento físico resultam em interconversão das isoformas de miosina de cadeia pesada de IIx para IIa (CAMPOS; LUECKE; WENDELN, 2002;KRAEMER;RATAMESS, 2004). Contrariamente, o destreinamento parece induzir a um aumento no percentual de isoformas de miosina tipo IIx, com um concomitante decréscimo nas isoformas IIa (ANDERSEN; AAGAARD, 2000). ...
... Entretanto, essa maior hidrólise de ATP leva, também, a maior produção de H + (próton hidrogênio), o que acaba contribuindo para redução do pH intramuscular e se tornando um dos possíveis mecanismos responsáveis pelo início da fadiga em exercícios de alta intensidade. Tal quadro poderia justificar o fato de o treinamento promover interconversões das isoformas IIa para as IIx, e o destreinamento, o caminho contrário (ANDERSEN; AAGAARD, 2000;CAMPOS;LUECKE;WENDELN, 2002;SARRAIPA, 2010;KRAEMER;RATAMESS, 2005). ...
... Eight slides were stained by ATPase histochemistry conducted at pH 9.4 after both alkaline (pH 10.30) and acid (pH 4.37, 4.53 and 4.58) pre-incubation [28,29]. ...
Background
The occurrence of hyperplasia, through myofibre splitting, remains a widely debated phenomenon. Structural alterations and fibre typing of skeletal muscle fibres, as seen during regeneration and in certain muscle diseases, can be challenging to interpret. Neuromuscular electrical stimulation can induce myofibre necrosis followed by changes in spatial and temporal cellular processes. Thirty days following electrical stimulation, remnants of regeneration can be seen in the myofibre and its basement membrane as the presence of small myofibres and encroachment of sarcolemma and basement membrane (suggestive of myofibre branching/splitting). The purpose of this study was to investigate myofibre branching and fibre type in a systematic manner in human skeletal muscle undergoing adult regenerative myogenesis.
Methods
Electrical stimulation was used to induce myofibre necrosis to the vastus lateralis muscle of one leg in 5 young healthy males. Muscle tissue samples were collected from the stimulated leg 30 days later and from the control leg for comparison. Biopsies were sectioned and stained for dystrophin and laminin to label the sarcolemma and basement membrane, respectively, as well as ATPase, and antibodies against types I and II myosin, and embryonic and neonatal myosin. Myofibre branches were followed through 22 serial Sects. (264 μm). Single fibres and tissue blocks were examined by confocal and electron microscopy, respectively.
Results
Regular branching of small myofibre segments was observed (median length 144 μm), most of which were observed to fuse further along the parent fibre. Central nuclei were frequently observed at the point of branching/fusion. The branch commonly presented with a more immature profile (nestin + , neonatal myosin + , disorganised myofilaments) than the parent myofibre, together suggesting fusion of the branch, rather than splitting. Of the 210 regenerating muscle fibres evaluated, 99.5% were type II fibres, indicating preferential damage to type II fibres with our protocol. Furthermore, these fibres demonstrated 7 different stages of “fibre-type” profiles.
Conclusions
By studying the regenerating tissue 30 days later with a range of microscopy techniques, we find that so-called myofibre branching or splitting is more likely to be fusion of myotubes and is therefore explained by incomplete regeneration after a necrosis-inducing event.
... Although %MHC isoform content does not measure muscle fiber diameters, it provides insight on the area of the muscle occupied by each major fiber type. 36,61,62 Consequently, a greater proportion of mCSA of the VL for the females was comprised of fibers that express type I characteristics. Therefore, the differences in the recorded MUAP AMPS can be partially explained by the proportion of fibers that expressed type I %MHC for MUs with RTs greater than 30% MVC. ...
Aims:
Motor unit recruitment and firing rate patterns of the vastus lateralis (VL) have not been compared between sexes during moderate- and high-intensity contraction intensities. Additionally, the influence of fiber composition on potential sex-related differences remains unquantified.
Methods:
Eleven males and 11 females performed 40% and 70% maximal voluntary contractions (MVCs). Surface electromyographic (EMG) signals recorded from the VL were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP ), initial firing rates (IFRs), mean firing rates (MFRs), and normalized EMG amplitude (N-EMGRMS ) at steady torque were analyzed. Y-intercepts and slopes were calculated for MUAPAMP , IFR, and MFR versus RT relationships. Type I myosin heavy chain isoform (MHC) was determined with muscle biopsies.
Results:
There were no sex-related differences in MU characteristics at 40% MVC. At 70% MVC, males exhibited greater slopes (p = 0.002) for the MUAPAMP , whereas females displayed greater slopes (p = 0.001-0.007) for the IFR and MFR versus RT relationships. N-EMGRMS at 70% MVC was greater for females (p < 0.001). Type I %MHC was greater for females (p = 0.006), and was correlated (p = 0.018-0.031) with the slopes for the MUAPAMP , IFR, and MFR versus RT relationships at 70% MVC (r = -0.599-0.585).
Conclusion:
Both sexes exhibited an inverse relationship between MU firing rates and recruitment thresholds. However, the sex-related differences in MU recruitment and firing rate patterns and N-EMGRMS at 70% MVC were likely due to greater type I% MHC and smaller twitch forces of the higher threshold MUs for the females. Evidence is provided that muscle fiber composition may explain divergent MU behavior between sexes.
... It is generally accepted that RE increases the proportion of IIa fibers in human skeletal muscle 88, 106 . It should be noted, though, that most RE-induced fiber transitions within this time course occurred by reducing the hybrid fibers and shifting them to a fiber type containing only one MyHC isoform 90 . ...
Purpose:
Skeletal muscle regulates health and performance by maintaining or increasing strength and muscle mass. Although the molecular mechanisms in response to resistance exercise (RE) significantly target the activation of protein synthesis, a plethora of other mechanisms and structures must be involved in orchestrating the communication, repair, and restoration of homeostasis after RE stimulation. In practice, RE can be modulated by variations in intensity, continuity and volume, which affect molecular responses and skeletal muscle adaptation. Knowledge of these aspects is important with respect to planning of training programs and assessing the impact of RE training on skeletal muscle.
Methods:
In this narrative review, we introduce general aspects of skeletal muscle substructures that adapt in response to RE. We further highlighted the molecular mechanisms that control human skeletal muscle anabolism, degradation, repair and memory in response to acute and repeated RE and linked these aspects to major training variables.
Results:
Although RE is a key stimulus for the activation of skeletal muscle anabolism, it also induces myofibrillar damage. Nevertheless, to increase muscle mass accompanied by a corresponding adaptation of the essential substructures of the sarcomeric environment, RE must be continuously repeated. This requires the permanent engagement of molecular mechanisms that re-establish skeletal muscle integrity after each RE-induced muscle damage.
Conclusion:
Various molecular regulators coordinately control the adaptation of skeletal muscle after acute and repeated RE and expand their actions far beyond muscle growth. Variations of key resistance training variables likely affect these mechanisms without affecting muscle growth.
... Muscle strength adaptations in preadolescence are more likely to occur at the neuromuscular level (Granacher et al. 2011) and training-induced changes in muscle size, at least in weightbearing muscles, seem not to play a crucial role. There are reports that preadolescent children show a tendency towards a lower percentage of fast-twitch fibres compared to adults (Oertel 1988;Dotan et al. 2012;Verdijk et al. 2014), which have been attributed a greater hypertrophic response to resistance training compared to slow-twitch fibres (Hortobágyi et al. 1996;Andersen and Aagaard 2000;Aagaard et al. 2001). Therefore, one might suggest that the lack of hypertrophy in our athletes could be related to a low percentage of fast-twitch fibres. ...
Purpose: Evidence on training-induced muscle hypertrophy during preadolescence is limited and inconsistent. Possible associations of muscle strength and tendon stiffness with jumping performance are also not investigated. We investigated the thickness and pennation angle of the gastrocnemius medialis muscle (GM), as indicators for potential muscle hypertrophy in preadolescent athletes. Further, we examined the association of triceps surae muscle–tendon properties with jumping performance. Methods: Eleven untrained children (9 years) and 21 similar-aged artistic gymnastic athletes participated in the study. Muscle thickness and pennation angle of the GM were measured at rest and muscle strength of the plantar flexors and Achilles tendon stiffness during maximum isometric contractions. Jumping height in squat (SJ) and countermovement jumps (CMJ) was examined using a force plate. We evaluated the influence of normalised muscle strength and tendon stiffness on jumping performance with a linear regression model. Results: Muscle thickness and pennation angle did not differ significantly between athletes and non-athletes. In athletes, muscle strength was greater by 25% and jumping heights by 36% (SJ) and 43% (CMJ), but Achilles tendon stiffness did not differ between the two groups. The significant predictor for both jump heights was tendon stiffness in athletes and normalised muscle strength for the CMJ height in non-athletes. Conclusion: Long-term artistic gymnastics training during preadolescence seems to be associated with increased muscle strength and jumping performance but not with training-induced muscle hypertrophy or altered tendon stiffness in the plantar flexors. Athletes benefit more from tendon stiffness and non-athletes more from muscle strength for increased jumping performance.
... MU conduction velocity has also been related to the greater proportion of type II fibres, due to their greater number of Na + /K + -ATPase pumps, which facilitate muscle A C C E P T E D membrane excitability and thus propagation of action potentials along the fibres (52). However, whilst some evidence exists for a greater number of type II fibres in elite weightlifters (53), longitudinal resistance training studies (14-19 weeks) have found no shifts in fibre type between type I to II (54,55), and fibre type composition has been found to be similar in untrained and bodybuilding groups (49, 50). Thus, the greater absolute recruitment thresholds and MU conduction velocity in resistance-trained individuals likely reflect the differences in muscle fibre size between the groups rather than any modifications in MU discharge characteristics or fibre type composition. ...
Purpose
Adjustments in motor unit (MU) discharge properties have been shown following short-term resistance training, however MU adaptations in long-term resistance-trained individuals are less clear. Here, we concurrently assessed MU discharge characteristics and MU conduction velocity in long-term resistance-trained (RT) and untrained (UT) men.
Methods
MU discharge characteristics (discharge rate, recruitment and derecruitment threshold) and MU conduction velocity were assessed after the decomposition of high-density electromyograms recorded from vastus lateralis (VL) and medialis (VM) of RT (>3 years; N = 14) and UT (N = 13) during submaximal and maximal isometric knee extension.
Results
RT were on average 42% stronger (maximal voluntary force, MVF: 976.7 ± 85.4 vs. 685.5 ± 123.1 N; p < 0.0001), but exhibited similar relative MU recruitment (VL: 21.3 ± 4.3 vs. 21.0 ± 2.3 %MVF; VM: 24.5 ± 4.2 vs. 22.7 ± 5.3 %MVF) and derecruitment thresholds (VL: 20.3 ± 4.3 vs. 19.8 ± 2.9 %MVF; VM: 24.2 ± 4.8 vs. 22.9 ± 3.7 %MVF; p ≥ 0.4543). There were also no differences between groups in MU discharge rate at recruitment and derecruitment, or at the plateau phase of submaximal contractions (VL: 10.6 ± 1.2 vs. 10.3 ± 1.5 pps, VM: 10.7 ± 1.6 vs. 10.8 ± 1.7 pps; p ≥ 0.3028). During maximal contractions of a subsample population (10 RT, 9 UT), MU discharge rate was also similar in RT compared to UT (VL: 21.1 ± 4.1 vs. 14.0 ± 4.5 pps, VM: 19.5 ± 5.0 vs. 17.0 ± 6.3 pps; p = 0.7173). MU conduction velocity was greater in RT compared to UT individuals in both VL (4.9 ± 0.5 vs. 4.5 ± 0.3 m.s-1; p < 0.0013) and VM (4.8 ± 0.5 vs. 4.4 ± 0.3 m.s-1; p < 0.0073).
Conclusions
RT and UT display similar MU discharge characteristics in the knee extensor muscles during maximal and submaximal contractions. The between-group strength difference is likely explained by superior muscle morphology of RT as suggested by greater MU conduction velocity.
... Antrenman boyunca sürekli bu kas lifi tipini aktifleştirince bu durum Tip IIa ve TipIIb kas lifi tiplerindeki geçişlere öncülük eder. İlginç olarak antrenmansızlık Tip IIb liflerinde artışa, Tip IIa liflerinde ise azalmaya neden olabilmektedir (Andersen, & Aagaard, 2000). Bilim adamları kas lifi tiplerindeki geçişin sadece aynı tip kas lifinde geçerli olabileceğini düşünmektedir. ...
... The existing heterogeneity amongst fibre types is reflected also in their ability to adapt to external stimuli (Edman et al., 2019;Horwath et al., 2020;Tannerstedt et al., 2009;Tesch, 1988;Verdijk et al., 2007). Given the large inter-individual variation in fibre type composition of human muscle (Horwath et al., 2021;Lexell et al., 1983), and its plasticity in response to different muscle loading patterns (Andersen & Aagaard, 2000;Staron et al., 1990), conducting investigations in a fibre type-specific manner to control for this variability is warranted. ...
Fibre type‐specific analyses are required for broader understanding of muscle physiology, but such analyses are difficult to conduct due to the extreme time requirements of dissecting and fibre typing individual fibres. Investigations are often confined to a small number of fibres from few participants with low representativeness of the entire fibre population and the participant population. To increase the feasibility of conducting large‐scale fibre type‐specific studies, a valid and rapid method for high‐throughput fibre typing of individually dissected fibres was developed and named THRIFTY (for high‐THRoughput Immunofluorescence Fibre TYping). Employing THRIFTY, 400 fibre segments were fixed onto microscope slides with a pre‐printed coordinated grid system, probed with antibodies against myosin heavy chain (MyHC)‐I and MyHC‐II and classified using a fluorescence microscope. The validity and speed of THRIFTY was compared to a previously validated protocol (dot blot) on a fibre‐to‐fibre basis. Fibre pool purity was evaluated using ‘gold standard’ SDS‐PAGE and silver staining. A modified THRIFTY‐protocol using fluorescence western blot equipment was also validated. THRIFTY displayed excellent agreement with the dot blot protocol, κ = 0.955 (95% CI: 0.928, 0.982), P < 0.001. Both the original and modified THRIFTY protocols generated type I and type II fibre pools of absolute purity. Using THRIFTY, 400 fibres were typed just under 11 h, which was approximately 3 times faster than dot blot. THRIFTY is a novel and valid method with high versatility for very rapid fibre typing of individual fibres. THRIFTY can therefore facilitate the generation of large fibre pools for more extensive mechanistic studies into skeletal muscle physiology. image
Key points
Skeletal muscle is composed of different fibre types, each with distinct physiological properties.
To fully understand how skeletal muscle adapts to external cues such as exercise, nutrition and ageing, fibre type‐specific investigations are required.
Such investigations are very difficult to conduct due to the extreme time requirements related to classifying individually isolated muscle fibres.
To bypass this issue, we have developed a rapid and reliable method named THRIFTY which is cheap as well as versatile and which can easily be implemented in most laboratories.
THRIFTY increases the feasibility of conducting larger fibre type‐specific studies and enables time‐sensitive assays where measurements need to be carried out in close connection with tissue sampling.
By using THRIFTY, new insights into fibre type‐specific muscle physiology can be gained which may have broad implications in health and disease.
... Because the longer this period, the lower the performance due to detraining. Researchers have found that detraining improves muscle peak power generation, muscle size and muscle neural drive and aerobic capacity at maximal muscle strength was found to be associated with a decrease in physiological, muscle function, such as a decrease [34,35,36,37,38,39]. In such a case, when the athlete returns to the eld, his performance decreases and the risk of injury increases at the same time. ...
During the pandemic period, football referees, like professional athletes, had to take a break from training for a long time. “Repetitive sprinting skill”, “high-intensity repetitive running performance” and “high aerobic power” have an important place in the performance of the referees, and it has been observed that the developments gained after 2 weeks in detraining situation begin to be lost. On the other hand, increased fat ratios and strength differences between the extremities are considered to be the risk of disability and low performance. The aim of this study is to ensure that the performances of elite athletes are preserved with resistance training when they are away from field training for a long time, such as during mandatory situations during the pandemic period, end of seasons, and during injury periods. Participants performed a study consisting of 24 AMRAP-style functional resistance training, limited to a maximum of 9 m ² area, with the aim of metabolic conditioning, and 12 injury-preventing exercises in 42 days. Age, height, body weight, and fat ratios were 35.6 ± 5.01 years, and 184.65 ± 4.42 cm, respectively. A total of 38 elite referees, 8 of whom were FIFA licensed, with a weight of 80.88 ± 7.12 kg and 12.9 ± 3.08%, participated. When the participants' pre-and post-exercise measurements were compared, post-exercise body weight (p = 0.017), fat percentage (p = 0.000), jump performance (p = 0.000), doggy running (p = 0.000), MaxVO 2 value (p = 0.000) and warm-up While there was a statistically significant difference in the RPE value after the procedure, no statistically significant difference was found in other parameters. As a result, it was found that planned functional strength training focused on metabolic conditioning significantly reduced anaerobic capacity and aerobic power losses in elite athletes. Accordingly, it is seen that home/hotel room training, which will be planned in holiday periods ranging from 1 to 3 months before starting the beginning of the season training, can be a simple and effective method for the athletes to start the next season in the readiest way.
... On average, 60 ± 18 type I, 60 ± 17 type IIA, and 8 ± 9 type IIX fibers were determined per time point and subject. Because IIX fibers became less abundant during the training period [70], and in some subjects, they were not detectable at all, we refer in our manuscript to type I and type IIA fibers and exclude IIX fibers from our analysis. In sum, 3137 type I and 3094 type IIA fibers were used for the analysis of the entire fiber population. ...
The acute resistance exercise (RE)-induced phosphorylation of mTOR-related signaling proteins in skeletal muscle can be blunted after repeated RE. The time frame in which the phosphor-ylation (p) of mTOR S2448 , p70S6k T421/S424 , and rpS6 S235/236 will be reduced during an RE training period in humans and whether progressive (PR) loading can counteract such a decline has not been described. Aim: (1) To enclose the time frame in which pmTOR S2448 , prpS6 S235/236 , and pp70S6k T421/S424 are acutely reduced after RE occurs during repeated RE. (2) To test whether PR will prevent that reduction compared to constant loading (CO) and (3) whether 10 days without RE may re-increase blunted signaling. Methods: Fourteen healthy males (24 ± 2.8 yrs.; 1.83 ± 0.1 cm; 79.3 ± 8.5 kg) were subjected to RE with either PR (n = 8) or CO (n = 6) loading. Subjects performed RE thrice per week, conducting three sets with 10-12 repetitions on a leg press and leg extension machine. Muscle biopsies were collected at rest (T0), 45 min after the first (T1), seventh (T7), 13th (T13), and 14th (X-T14) RE session. Results: No differences were found between PR and CO for any parameter. Thus, the groups were combined, and the results show the merged values. prpS6 S235/236 and pp70s6k T421/S424 were increased at T1, but were already reduced at T7 and up to T13 compared to T1. Ten days without RE re-increased prpS6 S235/236 and pp70S6k T421/S424 at X-T14 to a level comparable to that of T1. pmTOR S2448 was increased from T1 to X-T14 and did not decline over the training period. Single-fiber immunohistochemistry revealed a reduction in prpS6 S235/236 in type I fibers from T1 to T13 and a re-increase at X-T14, which was more augmented in type II fibers at T13 (p < 0.05). The entity of myofibers revealed a high heterogeneity in the level of prpS6 S235/236 , possibly reflecting individual contraction-induced stress during RE. The type I and II myofiber diameter increased from T0 and T1 to T13 and X-T14 (p < 0.05) Conclusion: prpS6 S235/236 and pp70s6k T421/S424 reflect RE-induced states of desensitization and re-sensitization in dependency on frequent loading by RE, but also by its cessation.
... Muscle fiber composition was analyzed as previously described. 68 Protein expression of glycogen synthase (GS), glycogen phosphorylase (GP), hexokinase II (HKII), glucose transporter protein 4 (GLUT4), and protein kinase B (Akt), adipose triglyceride lipase (ATGL), fatty acid translocase (FAT/CD36), long-chain fatty acid transport protein 4 (FATp4), plasma membrane fatty acidbinding protein (FATpm), perilipin 2 (PLN2), perilipin 3 (PLN3), perilipin 5 (PLN5), diglyceride acyltransferase (DGAT), and serine palmitoyltransferase (SPT) was performed by western blotting (for details, see Supporting Information). Analysis of enzyme activities of citrate synthase (CS) and 3-hydroxyacyl CoA dehydrogenase (HAD) was performed using approximately 2 mg of freeze-dried and dissected muscle tissue. ...
Aim & methods:
Extreme endurance exercise provides a valuable research model for understanding the adaptive metabolic response of older and younger individuals to intense physical activity. Here, we compare a wide range of metabolic and physiologic parameters in two cohorts of seven trained men, age 30±5 years or age 65±6 years, before and after the participants travelled ≈3000 km by bicycle over 15 days.
Results:
Over the 15-day exercise intervention, participants lost 2-3 kg fat mass with no significant change in body weight. V̇O2 max did not change in younger cyclists, but decreased (p=0.06) in the older cohort. The resting plasma FFA concentration decreased markedly in both groups, and plasma glucose increased in the younger group. In the older cohort, plasma LDL-cholesterol and plasma triglyceride decreased. In skeletal muscle, fat transporters CD36 and FABPm remained unchanged. The glucose handling proteins GLUT4 and SNAP23 increased in both groups. Mitochondrial ROS production decreased in both groups and ADP sensitivity increased in skeletal muscle in the older but not in the younger cohort.
Conclusion:
In summary, these data suggest that older but not younger individuals experience a negative adaptive response affecting cardiovascular function in response to extreme endurance exercise, while a positive response to the same exercise intervention is observed in peripheral tissues in younger and older men. The results also suggest that the adaptive thresholds differ in younger and old men, and this difference primarily affects central cardiovascular functions in older men after extreme endurance exercise.
... Another adaptive mechanism potentially contributing to the present improvement in 5-minute max cycling performance may be the shift from type IIx to type IIa myofibers generally observed with heavy-load resistance training (4,31), which has also been observed after prolonged (11-16 weeks) concurrent resistance and endurance training in well-trained (46,47) and top-level (National Team) (2) cyclists. This shift toward an increased proportion of oxidative and fatigue-resistant type IIa muscle fibers at the expense of reduced amounts of fatigable type IIx fibers may be beneficial for road cyclists, given that type IIa fibers are capable of producing high contractile power for more prolonged periods of time during racing events (13). ...
Bláfoss, R, Rikardo, J, Andersen, AØ, Hvid, LG, Andersen, LL, Jensen, K, Christensen, PM, Kvorning, T, and Aagaard, P. Effects of resistance training cessation on cycling performance in well-trained cyclists: an exploratory study. J Strength Cond Res 36(3): 796-804, 2022-Supplementary (i.e., concurrent) resistance training can enhance cycling performance among competitive cyclists. However, a lack of knowledge exists about the retention (decay profile) in mechanical muscle function and cycling performance after concurrent resistance and endurance training. The present exploratory intervention study investigated the effect of 6 weeks of resistance training cessation when preceded by 8 weeks of concurrent resistance and endurance training on mechanical muscle function and cycling performance in 9 male well-trained competitive cyclists (V̇o2max = 66 ± 7 ml·min-1·kg-1). Cyclists performed periodized resistance training targeting leg and core muscles for 8 weeks as a supplement to their normal endurance (cycling) training. This was followed by 6 weeks of endurance training only (retention period) leading up to the start of the competitive season. Maximal leg extensor power, isometric leg extensor strength (maximal voluntary contraction [MVC]), rate of force development (RFD), and long-term cycling performance (2-hour submaximal cycling at 55% of Wmax), followed by 5-minute max cycling were evaluated. After 8 weeks of concurrent resistance and endurance training, leg extensor power, MVC, and RFD increased by 12, 15, and 17%, respectively while mean power output (W) during 5-minute max cycling increased by 7% (p < 0.05). Training-induced gains in MVC and 5-minute max cycling power were retained after 6-week cessation of resistance training (p < 0.05). These findings indicate that competitive cyclists can focus on cycling training alone for at least 6 weeks leading up to competition without losing attained gains in maximal muscle strength and cycling performance achieved by preceding periods of concurrent resistance training.
... The slower intrinsic contractile properties of the LT-MST group relative to the untrained cohort were likely due to decreased myosin heavy-chain type IIX expression following prolonged maximum strength training. [36][37][38] Consistent with this idea individuals who have completed long-term maximum strength training have previously been documented to possess lower myosin heavy-chain type IIX expression than those who are untrained. 39 Indeed, when comparing the contractile properties of isolated rodent hindlimb muscles with high (extensor digitorum longus) and low (soleus) myosin heavy-chain type IIX expression, 40 those muscles with higher myosin heavychain type IIX expression display faster times to peak twitch force. ...
The purpose of this cross-sectional study was to compare explosive strength and underpinning contractile, hypertrophic and neuromuscular activation characteristics of long-term maximum strength trained (LT-MST; i.e. ≥3 years of consistent, regular knee extensor training) and untrained individuals. Sixty-three healthy young men (untrained [UNT] n=49, and LT-MST n=14) performed isometric maximum and explosive voluntary, as well as evoked octet knee extension contractions. Torque, quadriceps and hamstring surface EMG were recorded during all tasks. Quadriceps anatomical cross-sectional area (QACSAMAX; via MRI) was also assessed. Maximum voluntary torque (MVT; +66%) and QACSAMAX (+54%) were greater for LT-MST than UNT ([both] P<0.001). Absolute explosive voluntary torque (25-150 ms after torque onset; +41 to +64%; [all] P<0.001; 1.15≤ effect size [ES]≤2.36;) and absolute evoked octet torque (50 ms after torque onset; +43, P<0.001; ES=3.07) were greater for LT-MST than UNT. However, relative (to MVT) explosive voluntary torque was lower for LT-MST than UNT from 100-150 ms after contraction onset (-11% to -16%; 0.001≤P≤0.002; 0.98≤ES≤1.11). Relative evoked octet torque 50 ms after onset was lower (-10%; P<0.001; ES=1.14) and octet time to peak torque longer (+8%; P=0.001; ES=1.18) for LT-MST than UNT indicating slower contractile properties, independent from any differences in torque amplitude. The greater absolute explosive strength of the LT-MST group was attributable to higher evoked explosive strength, that in turn appeared to be due to larger quadriceps muscle size, rather than any differences in neuromuscular activation. In contrast, the inferior relative explosive strength of LT-MST appeared to be underpinned by slower intrinsic/evoked contractile properties.
... 7.0.1.0, GE Healthcare) as described previously (Andersen & Aagaard, 2000). ...
Statins are prescribed for the treatment of elevated cholesterol, but they may negatively affect metabolism, muscle performance, and the response to training. Coenzyme Q10 (CoQ10) supplementation may alleviate these effects. Combined simvastatin and CoQ10 treatment during physical training has never been tested. We studied the response to 8 weeks training (maximal oxygen uptake ( ), fat oxidation (MFO), the workload at which MFO occurred, and muscle strength) in statin naive dyslipidaemic patients who received simvastatin (40 mg/day) with (S + Q, n = 9) or without (S + Pl, n = 10) CoQ10 supplementation (2 × 200 mg/day) or placebo (Pl + Pl, n = 7) in a randomized, double‐blind placebo‐controlled study. and maximal workload increased with training (main effect of time, P < 0.05). MFO increased from 0.29 ± 0.10, 0.26 ± 0.10, and 0.38 ± 0.09 to 0.42 ± 0.09, 0.38 ± 0.10 and 0.48 ± 0.16 g/min in S + Q, S + Pl, and Pl + Pl, respectively (main effect of time, P = 0.0013). The workload at MFO increased from 75 ± 25, 56 ± 23, and 72 ± 17 to 106 ± 25, 84 ± 13 and 102 ± 31 W in S + Q, S + Pl, and Pl + Pl, respectively (main effect of time, P < 0.0001). Maximal voluntary contraction and rate of force development were unchanged. Exercise improved aerobic physical capacity and simvastatin with or without CoQ10 supplementation did not inhibit this adaptation. The similar increases in MFO and in the workload at which MFO occurred in response to training shows that the ability to adapt substrate selection and oxidation rates is preserved with simvastatin treatment, despite the potential negative impact of simvastatin at the mitochondrial level. CoQ10 supplementation does not augment this adaptation.
Key points
Simvastatins are prescribed for treatment of elevated cholesterol, but they may negatively affect metabolism, muscle performance and the response to training.
Coenzyme Q10 (CoQ10) supplementation may alleviate some of these effects.
We found that simvastatin treatment does not negatively affect training‐induced adaptations of substrate oxidation during exercise.
Likewise, maximal oxygen uptake increases with physical training also in patients in treatment with simvastatin.
CoQ10 supplementation in simvastatin‐treated patients presents no advantage in the adaptations to physical training
Simvastatin treatment decreases plasma concentrations of total CoQ10, but this can be alleviated by simultaneous supplementation with CoQ10
... Noteworthy, there appears to be dissociation after 16 weeks of inactivity, since we found a large decrease in maximal force while maximal power was not different from the previous weeks (Bosquet et al., 2013). Andersen and Aagaard (2000) provided some experimental data in healthy young males that could explain this discrepancy. Of all muscle fibres, type IIx represented 10.2 ± 2.5% at pretraining measurement time. ...
... Power training leads to increased muscle fibre pennation angle (58). This is important since it allows for greater increase of type II muscle fiber cross sectional area and composition (59). Power training also induces a slow (type I) to fast (type II) shift in MHC isoforms. ...
Journal of the International Society of Swimming Coaching 2(1) Fast swimming, either in the pool, in open water swimming, or in water polo, requires maximizing the efficiencies with which the human body can move through a liquid medium. A multitude of factors such as power and strength can affect the ability to swim fast as well as the final outcome. Strength and conditioning are tools used by sports scientists and coaches to enhance strength, power and, subsequently, to improve performance.
... Since its introduction by Thomas Delorme in 1940s [5], PBT has been studied and applied extensively, and proved to be an effective method by a huge body of researches. However, PBT has been criticized for the inherent limitations such as the complex process, risk of injury during the maximum strength test [6], and possible attenuation of type Ⅱ muscle fiber adaptation owing to the sets to failure [7,8], which may result in suboptimal training stimulus. ...
Background
There has been a surge of interest on velocity-based training (VBT) in recent years. However, it remains unclear whether VBT is more effective in improving strength, jump, linear sprint and change of direction speed (CODs) than the traditional 1RM percentage-based training (PBT).
Objectives
To compare the training effects in VBT vs. PBT upon strength, jump, linear sprint and CODs performance.
Data sources
Web of science, PubMed and China National Knowledge Infrastructure (CNKI).
Study eligibility criteria
The qualified studies for inclusion in the meta-analysis must have included a resistance training intervention that compared the effects of VBT and PBT on at least one measure of strength, jump, linear sprint and CODs with participants aged ≥16 yrs. and be written in English or Chinese.
Methods
The modified Pedro Scale was used to assess the risk of bias. Random-effects model was used to calculate the effects via the mean change and pre-SD (standard deviation). Mean difference (MD) or Standardized mean difference (SMD) was presented correspondently with 95% confidence interval (CI).
Results
Six studies met the inclusion criteria including a total of 124 participants aged 16 to 30 yrs. The differences of training effects between VBT and PBT were not significant in back squat 1RM (MD = 3.03kg; 95%CI: -3.55, 9.61; I ² = 0%) and load velocity 60%1RM (MD = 0.02m/s; 95%CI: -0.01,0.06; I ² = 0%), jump (SMD = 0.27; 95%CI: -0.15,0.7; I ² = 0%), linear sprint (MD = 0.01s; 95%CI: -0.06, 0.07; I ² = 0%), and CODs (SMD = 0.49; 95%CI: -0.14, 1.07; I ² = 0%).
Conclusion
Both VBT and PBT can enhance strength, jump, linear sprint and CODs performance effectively without significant group difference.
... At the same time, it is important to emphasize that both groups experienced an increase in muscle mass after the training period, indicating that postmenopausal women can increase their muscle mass by performing regular resistance training both with and without ET. Resistance training leads to a reduction in the MHC IIx (Andersen and Aagaard, 2000). Our data showed significant downregulation of MHC IIx protein in the PLC group and a numeric downregulation in the ET group compared with baseline. ...
Context
Women show an accelerated loss of muscle mass around menopause, possibly related to the decline in estrogen. Furthermore, the anabolic response to resistance exercise seems to be hampered in postmenopausal women.
Objective
We aimed to test the hypothesis that transdermal estrogen therapy (ET) amplifies the skeletal muscle response to resistance training in early postmenopausal women.
Design
A double-blinded randomized controlled study.
Setting
Department of Public Health, Aarhus University, Denmark.
Participants
Thirty-one healthy, untrained postmenopausal women no more than 5 years past menopause.
Intervention(s)
Supervised resistance training with placebo (PLC, n = 16) or transdermal ET ( n = 15) for 12 weeks.
Main Outcome Measure(s)
The primary outcome parameter was a cross-sectional area of quadriceps femoris measured by magnetic resonance imaging, and secondary parameters were fat-free mass (dual-energy X-ray absorptiometry), muscle strength, and functional tests.
Results
The increase in muscle cross-sectional area was significantly greater in the ET group (7.9%) compared with the PLC group (3.9%) ( p < 0.05). Similarly, the increase in whole-body fat-free mass was greater in the ET group (5.5%) than in the PLC group (2.9%) ( p < 0.05). Handgrip strength increased in ET ( p < 0.05) but did not change in the PLC group. Muscle strength parameters, jumping height, and finger strength were all improved after the training period with no difference between groups.
Conclusion
The use of transdermal ET enhanced the increase in muscle mass in response to 12 weeks of progressive resistance training in early postmenopausal women.
... It is known that low rates of physical activity, typical of people with disabilities, trigger deconditioning with disuse-induced changes in muscle [41,42]. These changes include increased ROS production, Ca 2+ alterations and release of proteolytic agents with fiber atrophy and reduced muscle mass [43], muscle fiber phenotype changes with marked decrease in mitochondrial enzyme activities and lower oxidative capacity [8,42,44,45], and decreases in capillary supply and blood flow in unloaded muscles [46]. The combination of unfavorable adaptive factors may also stimulate the conversion of pyruvate into lactate, even in the presence of oxygen [8] with greater lactate and H+ accumulation during exercise [42]. ...
Abnormal levels of pyruvate and lactate were reported in multiple sclerosis (MS). We studied the response of markers of mitochondrial function to rehabilitation in relation to type, intensity and endurance performance in severely disabled MS patients. Forty-six progressive MS patients were randomized to receive 12 walking sessions of robot-assisted gait training (RAGT, n = 23) or conventional overground therapy (CT, n = 23). Ten healthy subjects were also studied. Blood samples were collected to determine lactate, pyruvate, and glutathione levels and lactate/pyruvate ratio pre–post rehabilitation. In vivo muscle metabolism and endurance walking capacity were assessed by resting muscle oxygen consumption (rmVO2) using near-infrared spectroscopy and by six-minute walking distance (6MWD), respectively. The levels of mitochondrial biomarkers and rmVO2, altered at baseline with respect to healthy subjects, improved after rehabilitation in the whole population. In the two groups, an enhanced response was observed after RAGT compared to CT for lactate (p = 0.012), glutathione (<0.001), lactate/pyruvate ratio (p = 0.08) and rmVO2 (p = 0.07). Metabolic biomarkers and 6MWD improvements were exclusively correlated with a training speed markedly below individual gait speed. In severely disabled MS patients, rehabilitation rebalanced altered serum metabolic and muscle parameters, with RAGT being more effective than CT. A determinable slow training speed was associated with better metabolic and functional recovery. Trial Registration: ClinicalTrials.gov NCT02421731.
... Myosin heavy chain composition. Prolonged resistance training has been previously shown to induce MHC IIa upregulation and MHC IIx downregulation (4). However, only the OC users revealed a significant shift from MHC IIx to MHC IIa after the training intervention. ...
Objective: to determine whether skeletal muscle molecular markers and SC number were influenced differently in users and non-users of oral contraceptives (OCs) following 10 weeks of resistance training Methods: Thirty-eight young healthy untrained users (n=20) and non-users of OC (n=18) completed a 10-week supervised progressive resistance training program. Before and after the intervention a muscle tissue sample was obtained from the vastus lateralis muscle for analysis of muscle fiber cross sectional area (fCSA), and satellite cell (SC) and myonuclei number using immunohistochemistry, gene expression using PCR, protein expression and myosin heavy chain composition. Results: Following the training period quadriceps fCSA (p<0.05), SCs/ type I fiber (p=0.05) and MURF-1 mRNA (p<0.01) were significantly increased with no difference between the groups. However, SCs/total fiber and SCs/type II fiber increased in OC users only, and SCs/ type II fCSA tended (p=0.055) to be greater in the OC-users. Furthermore, in OC users there were a fiber type shift from MHC IIx to MHC IIa (p<0.01) and expression of MRF4 mRNA (p<0.001) was significantly greater than in non-OC users. Conclusion: Use of 2nd generation OCs in young untrained women increased skeletal muscle MRF4 expression and SC number following 10 weeks of resistance training compared to non-users.
... Muscle strength adaptations in preadolescence are more likely to occur at the neuromuscular level (Granacher et al. 2011) and training-induced changes in muscle size, at least in weightbearing muscles, seem not to play a crucial role. There are reports that preadolescent children show a tendency towards a lower percentage of fast-twitch fibres compared to adults (Oertel 1988;Dotan et al. 2012;Verdijk et al. 2014), which have been attributed a greater hypertrophic response to resistance training compared to slow-twitch fibres (Hortobágyi et al. 1996;Andersen and Aagaard 2000;Aagaard et al. 2001). Therefore, one might suggest that the lack of hypertrophy in our athletes could be related to a low percentage of fast-twitch fibres. ...
Purpose: Evidence on training-induced muscle hypertrophy during preadolescence is limited and inconsistent. Possible associations of muscle strength and tendon stiffness with jumping performance are also not investigated. We investigated the thickness and pennation angle of the gastrocnemius medialis muscle (GM), as indicators for potential muscle hypertrophy in preadolescent athletes. Further, we examined the association of triceps surae muscle-tendon properties with jumping performance.
Methods: Eleven untrained children (9 years) and 21 similar-aged artistic gymnastic athletes participated in the study. Muscle thickness and pennation angle of the GM were measured at rest and muscle strength of the plantar flexors and Achilles tendon stiffness during maximum isometric contractions. Jumping height in squat (SJ) and countermovement jumps (CMJ) was examined using a force plate. We evaluated the influence of normalised muscle strength and tendon stiffness on jumping performance with a linear regression model.
Results: Muscle thickness and pennation angle did not differ significantly between athletes and non-athletes. In athletes, muscle strength was greater by 25% and jumping heights by 36% (SJ) and 43% (CMJ), but Achilles tendon stiffness did not differ between the two groups. The significant predictor for both jump heights was tendon stiffness in athletes and normalised muscle strength for the CMJ height in non-athletes.
Conclusion: Long-term artistic gymnastics training during preadolescence seems to be associated with increased muscle strength and jumping performance but not with training-induced muscle hypertrophy or altered tendon stiffness in the plantar flexors. Athletes benefit more from tendon stiffness and non-athletes more from muscle strength for increased jumping performance.
... The discrepancies with other previous work could be linked to the different muscles analysed (vastus lateralis, deltoids, biceps and triceps brachii), to the training protocol and to the possible intake of anabolic compounds. Regarding myosin isoforms expression and fibre type distribution, many reports have suggested that RT causes a 2X to 2A shift, [77][78][79][80] and this was confirmed in a BB population by Kesidis and colleagues, 81 who found increased percentages of 2A and 1-2A fibres, with lower 2X fibres percentage in BB compared to CTRL. Our results were in agreement, as the proportion of fibres expressing 2A myosin was significantly higher in BB compared to CTRL, at expenses of both 2X fibres and slow fibres. ...
Aim:
Skeletal muscles of Body Builders (BB) represent an interesting model to study muscle mass gains in response to high volume resistance training. It is debated whether muscle contractile performance improves in proportion to mass. Here we aim to assess whether muscle hypertrophy does not occur at the expense of performance.
Methods:
6 BB and 6 untrained controls (CTRL) were recruited. Cross Sectional Area (CSA) and maximum voluntary contraction (MVC) of quadriceps femoris muscle (QF) and CSA and architecture of vastus lateralis (VL) were determined. Moreover, a biopsy was taken from VL mid-portion and single fibres were analysed.
Results:
QF CSA and MVC were 32% (n.s., P=.052) and 58% (P=.009) higher in BB than in CTRL, respectively. VL CSA was 37% higher in BB (P=.030). Fast 2A fibres CSA was 24% (P=.048) greater in BB than in CTRL, when determined in immunostained sections of biopsy samples. Single permeabilized fast fibres CSA was 37% (n.s., P=.052) higher in BB than in CTRL, and their force was slightly higher in BB (n.s.), while specific tension (P0 ) was 19% (P=.024) lower. The lower P0 was not explained neither by lower myosin content nor by impaired calcium diffusion. Conversely, the swelling due to skinning-induced permeabilization was different and, when used to correct P0 , differences between populations disappeared.
Conclusions:
The results show that high degree of muscle hypertrophy is not detrimental for force generation capacity, as increases in fibre size and force are strictly proportional once the differential swelling response is accounted for.
... This is in contrast to previous findings where improved peak power output (Fortes et al., 2019) and muscle strength (Martin et al., 1994) were found from short periods (2-4 weeks) of reduced training volume and maintained intensity-distribution in well-trained cyclists and runners. Inactivity has previously been reported to change fiber-type distribution toward type IIX phenotype (Coyle et al., 1985;Andersen and Aagaard, 2000). Hypothetically, an absence of type II muscle fiber activation as might be assumed during 3 weeks of LIT only and an absence of muscular activation might therefore favor a switch in fiber-specific characteristics, toward a more fast-twitch phenotype, possibly explaining an improved V max in CON. ...
The purpose of this study was to investigate the effects of including 30-s sprints in one weekly low-intensity training (LIT) session during a 3-wk transition period in elite cyclists. Sixteen male elite cyclists (maximal oxygen uptake, VO2max: 72±5 mL·kg-1·min-1) reduced their training load by ~60% for 3 wks from the end of competitive season and performed only LIT (CON) or included 30-s sprints in one weekly LIT-session (SPR). Performance and physiological capacities were evaluated during a prolonged (~2.5 hrs) test-session, including a strength test, a submaximal blood lactate profile test, an incremental test to exhaustion to determine VO2max, 1 h continuous cycling including 4 maximal 30-s sprints, and a 20-min all-out test. In addition, mental recovery was evaluated using the Athlete Burnout Questionnaire. The only significant between-group change during the transition period was an 8±11% larger improvement in 30-s sprint performance in SPR compared to CON (SPR: 4±5%, CON: -4±5%, p= .01). Although not different from CON, SPR maintained 20-min all-out performance (-1±5%, p= .37) and fractional utilization of VO2max (1.9±6.1 %-points, p= .18) during the 20-min all-out test, whereas corresponding declines were observed in CON (-3±5%, p= .04, and -2.5±2.9 %-points, p= .02, respectively). Power output at 4 mmol·L-1 blood lactate concentration decreased similarly in SPR (-4±4%, p= .02) and CON (-5±5%, p= .01), while VO2max, maximal aerobic power (Wmax), and total burnout score were unaffected in both groups. Including sprints in one weekly LIT-session in the transition period improves sprint performance and maintains 20-min all-out power and fractional utilization of VO2max without compromising mental recovery. Inclusion of sprints in LIT-sessions may therefore be a plausible, time-efficient strategy during short periods of reduced training.
... The vast majority of the published studies on "detraining effect" (or reduction in exercise training volume) on physical performance, body composition and skeletal muscle physiology and biochemistry, involved athletes and physically-active populations [28,29], whilst data are available also from bed rest studies [30] and studies on astronauts [31]. Briefly, these findings report significant reductions in cardiorespiratory capacity [29], muscle strength and power, alternations in muscle fiber type (i.e. from IIa to IIx) [32] and changes in enzyme content and mitochondrial-related parameters within the skeletal muscle [33,34], reductions in muscle mass and increases in fat mass [28] and changes in blood lipids profile [28]. ...
PurposeLimited data exist regarding the effects of detraining on functional capacity and quality of life (QoL) in the hemodialysis population. The aim of the current study was to assess whether the discontinuation from a systematic intradialytic exercise training program will affect aspects of health-related QoL and functional capacity in hemodialysis patients.Methods
Seventeen hemodialysis patients (12 Males/5 Females, age 60.8 ± 13.6 year) participated in this study. Patients were assessed for functional capacity using various functional capacity tests while QoL, daily sleepiness, sleep quality, depression and fatigue were assessed using validated questionnaires at the end of a 12-month aerobic exercise program and after 12 months of detraining.ResultsThe detraining significantly reduced patients’ QoL score by 20% (P = 0.01). More affected were aspects related to the physical component summary of the QoL (P < 0.001) rather than those related to the mental one (P = 0.096). In addition, the performance in the functional capacity tests was reduced (P < 0.05), while sleep quality (P = 0.020) and daily sleepiness scores (P = 0.006) were significantly worse after the detraining period. Depressive symptoms (P = 0.214) and the level of fatigue (P = 0.163) did not change significantly.Conclusions
Detraining has a detrimental effect in patients’ QoL, functional capacity and sleep quality. The affected physical health contributed significantly to the lower QoL score. It is crucial for the chronic disease patients, even during emergencies such as lockdowns and restrictions in activities to maintain a minimum level of activity to preserve some of the acquired benefits and maintain their health status.
... Given that there is evidence to suggest that NO 3 − supplementation may be more effective at enhancing physiological responses in type II muscle fibers [124] and since the proportion of type II muscle fibers may be greater in the upper body musculature, i.e., [125], this might account for the improved bench press and the inconsistent effects observed on squat performance after NO 3 − supplementation. However, there is evidence that weightlifting training increases both the hypertrophy and proportion of type II muscle fibers, such that the proportion of type II muscle is greater in resistance-trained individuals [126,127]. Accordingly, this could partly account for the improvements observed in Mosher et al. [116], Williams et al. [113] and Ranchal-Sánchez et al. [114], who recruited resistance-trained men. Taken together, the existing, albeit limited, evidence suggests that acute and short-term dietary NO 3 − supplementation can enhance weightlifting exercise performance by increasing muscle power production, velocity of contraction and muscular endurance in healthy resistance-trained adults. ...
Dietary nitrate (NO 3 −) supplementation has been evidenced to induce an ergogenic effect in endurance and sprint-type exercise, which may be underpinned by enhanced muscle contractility and perfusion, particularly in type II muscle fibers. However, limited data are available to evaluate the ergogenic potential of NO 3 − supplementation during other exercise modalities that mandate type II fiber recruitment, such as weightlifting exercise (i.e., resistance exercise). In this systematic review, we examine the existing evidence basis for NO 3 − supplementation to improve muscular power, velocity of contraction, and muscular endurance during weightlifting exercise in healthy adults. We also discuss the potential mechanistic bases for any positive effects of NO 3 − supplementation on resistance exercise performance. Dialnet, Directory of Open Access Journals, Medline, Pubmed, Scielo, Scopus and SPORT Discus databases were searched for articles using the keywords: nitrate or beetroot and supplement or nut*r or diet and strength or "resistance exercise" or "resistance training" or "muscular power". Four articles fulfilling the inclusion criteria were identified. Two of the four studies indicated that NO 3 − supplementation could increase aspects of upper body weightlifting exercise (i.e., bench press) performance (increases in mean power/velocity of contraction/number of repetitions to failure), whereas another study observed an increase in the number of repetitions to failure during lower limb weightlifting exercise (i.e., back squat). Although these preliminary observations are encouraging, further research is required for the ergogenic potential of NO 3 − supplementation on weightlifting exercise performance to be determined.
... This postulate is based on the fact that the weightlifters require skill in order to carry out their discipline and therefore may be able to reduce the amount of co contraction present during an isometric test of strength. Previously Aagaard et al. (2000) has shown that the level of co contraction is reduced in resistance trained subjects. Therefore the untrained group may be less able to generate isometric force due to an inability to control the co contraction of the antagonistic muscles in comparison to the weightlifters. ...
This thesis has developed and utilised an inertial loading system to study human skeletal muscle power output. Specifically, the apparatus has been used to study the effects of different modes of exercise, muscle myosin isoform composition and the effects of ageing on the ability of the lower limb muscles to generate explosive power. A variable inertial loading system was designed and constructed which allowed for the sensitive detection of the rotational properties of a flywheel from which the contractile characteristics of muscle could be inferred. When housed in the Nottingham Power Rig (NPR) the peak power generated by young non-trained male subjects from a single lower limb thrust ranged from 608 - 965 Watts and was found to occur at inertial loads ranging from 0.09 - 0.22 kgm2. To investigate the low power outputs observed at the low inertial loads, where the contraction time was short, a pre release mechanism was incorporated into the flywheel assembly. Significant increases in power output of ~ 17% were achieved at the lowest inertial load (P = 0.02), if a prior build up of isometric torque was allowed prior to movement. This suggested that at the low inertial loads, without the pre release, insufficient time was allowed for the muscle to generate its maximum power output. The flywheel system was incorporated into a cycle ergometer to allow power - velocity characteristics to be examined during inertial sprint cycling. Peak power obtained in young subjects (n = 9) was significantly higher in the cycle exercise when compared with the NPR (1620 vs. 937 Watts). In contrast to the NPR where a parabolic relationship between power and inertial load was observed, during sprint cycling power plateaued above a 'critical' load. It was concluded that the repetitive acceleration of inertial loads, above this critical threshold, will always allow the expression of peak power during cycling as ultimately a velocity will be achieved which corresponds to that required for peak power generation. An analysis of the myosin heavy chain (MHC) isoform composition of the vastus lateralis muscle was performed in young and elderly male subjects (n = 14, mean age 29.4 and 73.8). The percentage MHC-II isoform composition was significantly lower in the older subjects as was the velocity at which peak power occurred (Vopt). Overall the Vopt during sprint cycling was found to be related to the percentage MHC-II composition of the vastus lateralis (R = 0 .82, P<0.001). Finally, muscle power was examined in Elite level master Olympic weightlifters (n = 54, aged 40 - 87 years) and aged matched controls. On average the weightlifters generated ~ 32% more peak power than their aged matched counterparts and required significantly higher inertial loads to express their peak power output. In spite of 'load optimisation', power declined at twice the rate of strength. The levels of power suggest a 20 year advantage for the weightlifters.
... DCER involving both lengthening and shortening MTU actions through a full ROM has been studied from several aspects of neuroplasticity and neuromechanical development (Aagaard et al., 2002). DCER at higher intensities or loads has been shown to elicit an increase in type IIA MHC expression (Andersen and Aagaard, 2000), type II muscle fiber CSA (Aagaard et al., 2001), and peak force and power of all fiber types (Widrick et al., 2002). Other combined training programs that included DCER and loaded ballistic exercises have seen improvements in RFD, maximal strength, and jumping performance (Kyrolainen et al., 2005), interestingly with no apparent changes in titin isoform expression. ...
Athletic performance is determined by numerous variables that cannot always be controlled or modified. Due to aesthetic requirements during sports such as dance, body alignment constrains possible movement solutions. Increased power transference around the ankle-joint, coupled with lower hip-joint power, has become a preferential strategy in dancers during leaps and may be considered a dance-specific stretch-shortening cycle (SSC) demand. Newell's theoretical model of interacting constraints includes organismic (or individual), environmental, and task constraints describing the different endogenous and exogenous constraints individuals must overcome for movement and athletic performance. The unique task constraints imposed during dance will be used as a model to justify an isolated joint, single-targeted block progression training to improve physical capacity within the context of motor behavior to enhance dance-specific SSC performance. The suggested ankle-specific block progression consists of isometrics, dynamic constant external resistance, accentuated eccentrics, and plyometrics. Such programming tactics intend to collectively induce tendon remodeling, muscle hypertrophy, greater maximal strength, improved rate of force development, increased motor unit firing rates, and enhanced dynamic movement performance. The current perspective provides a dualistic approach and justification (physiological and motor behavioral) for specific strength and conditioning programming strategies. We propose implementation of a single-targeted block progression program, inspired by Newell's theoretical model of interacting constraints, may elicit positive training adaptations in a directed manner in this population. The application of Newell's theoretical model in the context of a strength and conditioning supports development of musculoskeletal properties and control and is conceptually applicable to a range of athletes.
... Antrenman boyunca sürekli bu kas lifi tipini aktifleştirince bu durum Tip IIa ve TipIIb kas lifi tiplerindeki geçişlere öncülük eder. İlginç olarak antrenmansızlık Tip IIb liflerinde artışa, Tip IIa liflerinde ise azalmaya neden olabilmektedir (Andersen, & Aagaard, 2000). Bilim adamları kas lifi tiplerindeki geçişin sadece aynı tip kas lifinde geçerli olabileceğini düşünmektedir. ...
Sporda başarılı olabilmenin altın anahtarı hiç kuşku yok ki bilimsel çalışmalardan elde edilmiş veriler kullanılarak dizayn edilmiş antrenmanların uygulanmasıdır. Tarih boyunca spor bilim insanlarının ilgisini çeken konulardan bir tanesi de sporcuların vücut yapısı ile performansları arasındaki ilişki olmuştur. Sporda arzu edilen üstün performansa ulaşabilmek için, iyi planlanmış uygun antrenman programının yanı sıra, antropometrik ve fizyolojik yapıya da dikkat edilmelidir Aksi taktirde fiziksel yapının özelliği, icra edilen spor dalına uygun olmadıkça sporcunun performansı en uygun düzeyde gerçekleşmesi düşünülemez. Antropometri; insan bedeninin özelliklerini belirli ölçme yöntemleri ve ilkeleriyle, boyutlarına veya yapı özelliklerine göre sınıflandıran bir tekniktir (Yazarer ve ark.,2004). Antropometrik veriler, çeşitli ırklar, etnik gruplar, farklı sosyoekonomik toplumlar, cinsiyetler arasında değişim ve gelişim evreleri içinde farklılıklar gösterirler (Günay ve ark.,2006). Antropometrik özelliklerin performansa etkisi, beden yapısı, kompozisyonu, ağırlık ve boy, motor işlevlerde ve performansta önemli faktörler olarak kabul edilmektedirler. Beden ölçüsünün göstergesi olan ağırlık, boy, yaş ve cinsiyet gibi değişkenlerle kombine edilerek, normlar geliştirilmiştir. Bu normlar, birçok bedensel aktivitede rol alan çocuk ve gençlerin hangi gruba uygunluk gösterdiğinin bilinmesi açısından yararlı olmuştur. Antropometrik ölçülerin motorik performansla ilişkili olduğu ve performans düzeylerindeki potansiyel etkinliği fark edilmistir (Can ve ark., 2002). Antropometri son yıllarda sporda oldukça kullanışlı bir alan olarak ortaya çıkmaktadır. Spor dalının özelliklerine göre elit sporcunun morfolojik yapısının belirlenmesinde de önemli bir rol oynamaktadır (Pekel, 2004; Savucu ve ark., 2004). İnsan vücudunun dış görünüşünün sınıflandırılması veya vücut tipinin belirlenmesine somatotip denir. Adolesan dönemi futbolcuların performans düzeylerinin artırılması için somatotiplerinin belirlenmesi gerekir. Çünkü sporcuların fiziksel özellik ve yeteneklerinin tespit edilmesi, sporcu seçiminde ve uygun antrenman programının planlanmasında önemli bilgiler sağlayabilir (Can ve ark., 2002). Sahip olunan fiziksel yapının özelliği yapılan spor dalına uygun olmadıkça istenilen performans düzeyine ulaşmak pek mümkün değildir. Fiziksel yapı bir sporcunun yüksek düzeyde performans gösterebilmesinin göstergelerinden sadece bir tanesidir ve kuvvet, güç, esneklik, sürat, dayanıklılık ve çabukluk gibi diğer performans göstergeleriyle birleşerek sporcunun performansını olumlu yönde etkilemektedir (Acar, 2000). Beden ölçüsü, beden yapısı ve kompozisyonu, kuvvet ve performansı etkileyen önemli faktörlerdir. Çocuklarda kas kuvvetinin artışı yaşa, cinsiyete, olgunlaşma düzeyine, önceki fiziksel etkinlik düzeyine ve beden ölçülerine bağlıdır (Duquet ve Carter, 1996). Morfolojik yapı kişiler arasında farklılık gösterir. Yıllarca gerçekleştirilen araştırmalar ile ortaya çıkarılan farklı insan vücut şekilleri çeşitli faktörlerden bağımsız kalıcı karakteristiklerine göre sınıflandırılmış ve somatotip yapı ile motorik özellikler ve psişik yapı arasında önemli ilişkiler tespit edilmiştir. Fiziksel yetenekler ile somatotip bileşenleri arasındaki ilişkilerin araştırıldığı çalışmalarda dayanıklılık, kuvvet, hız gibi fiziksel yetenekler ile mezomorfi bileşeni arasında pozitif, endomorfi bileşeni negatif etkiler dikkat çekmektedir (Gürses ve Olgun, 1991). Diğer spor branşları gibi futbolda da, başarıda teknik ve taktik kabiliyetlerin yanında antropometrik özellikler ve fiziki performans da önemli faktörlerdendir (Hakinken, 1992; . Laessens, 1987). Bugün tüm dünyada oynandığı her yerde yüz binlerce insanı statlara ve televizyon ekranları basına çeken, onlara aynı anda heyecan, sevinç ve üzüntüyü yaşatan futboldan kitlelerin beklentileri artmaktadır. Özellikle medyanın yakından ilgilendiği uygulayıcısından çok seyirci kitlesinin daha yoğun olduğu bir gerçektir. Bu yüzden futbolda bilimsel araştırmalara hız verilmistir (Zorba ve ark., 1999). Futbol oyunu, oyuncunun teknik, taktik, özelliklerinin yanı sıra antropometrik ve fizyolojik uygunluğuyla direkt ilişkilidir. Bu ilişkilerin daha iyi belirlenmesi amacıyla, oyuncuların oyun esnasındaki hareketleri incelenmiş, bu hareketler futbolcuların fizyolojik profilinin belirlenmesinde önemli bir etken olmuştur (Carter ve Heath, 1990). Çocuk ve futbol konusunda büyüme ve gelişme dikkat edilmesi gereken en önemli unsurlardandır. Çocuk büyüdükçe ve geliştikçe futbol performansı da artacaktır. Çocukların fiziksel büyüme ve gelişmesi aerobik ve anaerobik kapasitesini, kas kuvvetini, süratini ve çabukluğunu etkileyecektir dolayısıyla yas ilerledikçe futbolcu maç sırasında daha hızlı, daha dayanıklı ve daha kuvvetli olacaktır (TFF Çocuk ve Futbol, 2009).Sporda başarılı olmak için eğitimcilerin ve uzmanların yetişen çocukların fiziki özelliklerini iyi tanımaları ve iyi analiz etmeleri gerekmektedir. Antropometrik özellikler, insanın anatomik yapısı olup, gövde ile üyeler arasında orantılıdır. Antropometrik özellikler antrenman ile kazanılmaz. Sporcuda verimi etkileyen özelliklerin başında gelmektedir. Bu nedenle yetenekli ve spor dalına uygun kişileri bulmak önemlidir (Yörükoğlu ve Koz,2007). Bu araştırmanın amacı, büyük bir genç nüfus potansiyeline sahip olan ülkemizde çocukların ve gençlerin spora yönlendirilmesinde, antropometrik ölçümler yardımıyla somatotiplerinin hesaplanması ve performans özelliklerinin belirlenerek, kişiye uygun spor dalı seçiminin yapılması ve bu alandaki çalışmalara katkıda bulunmaktır. Bu bilgiler ışığı altında çalışmamız aracılığı ile erkek öğrencilerin antropometrik, somatotip ve performans özelliklerini belirleyerek futbolda yetenek seçimi ve yönlendirme sürecinde sporcu seçiminde ve yine bu alanda gerçekleştirilecek çalışmalara katkı sağlayacağı düşünülmektedir.
... (2001) tarafından yapılan çalışmada, bulunan veriler, KGO ve kontraktif impuls hızının yol açtığı artışları kanıtlamaktadır. Deneklerin grupları incelendiğinde tip-2 kas liflerinde hipertrofinin gözlemlendiği, ancak toplam tip tipi kompozisyonlarında bir değişikliğe rastlanılmadığı bildirilmiştir (Andersen, 2000). Ek olarak, kas lifi pennasyon açısının arttığı; bununda, fizyolojik kas lifi alanında ve maksimum kasılma kuvvetinde bir artışa neden olduğu söylenmiştir (Aagaard, 2001). ...
The aims of this study were to determine the differences in force, power and rate of peak force development applied at different loads in Olympic lift variations and to calculate the optimal load by finding the optimal power output at different loads. 10 male athletes (mean age, 25.5 ± 1.4 years; mean height, 182.1 ± 3.4cm; mass average; 84.5 ± 6.2kg; 1TM hang power clean weights; 84 ± 13.7), who had an exercise
experience for at least three years and could apply Olympic lifting variations, were participated this study voluntarily. Athletes were asked to perform mid-thigh high pull (MTHP) and hang power clean (HPC) exercises at 60% -70% -80% and 90% loads according to their previously received ‘1 repetition maximum (RM) Hang power
clean’ performance. Qualisys Track Manager (Version 2.12) which was a three dimensional motion analysis software were used for collecting kinematic parameters during lifting performances. Reflector markers were attached to the athletes and T calibration method was used for the field calibration. The obtained kinematic data values such as velocity an acceleration, also power, force and rate of peak force
development ratios were calculated and analyzed in SPSS 19.0 (SPSS Inc., Chicago, IL, USA) program. In findings, there were significant differences between the force, power and rate of peak force development between the two different variations of
lifting (p<0.05). When the differences in force values between the two lifting variations were examined, a significant difference was also found. In power values, there were significantly differences at only 60% and 70% of 1RM values (p <0.05). Lastly, there were significant differences between the two variations of lifting in all loads except 60% of 1RM (p<0.05). As for the determination of the optimal load in
selected exercises, another part of the study, the optimal load for Hang Power Clean was determined in 80% of 1RM and Mid-thigh High Pull in 70% of 1RM. In conclusion, according to the findings, it is clear that Olympic lifting variations produce high data in terms of force, power and rate of peak force development. As a result of X
the answers to the questions sought in the study, the data revealed that Olympic lift variations for power development are ideal exercises for maximal power output, rate of force development, maximal power output, such as optimal load differences between exercises and speed-strength and strength-speed in athletes training. It is thought that they will be able to make performance contributions with these data in their training plans for their development.
... The discrepancies with other previous work could be linked to the different muscles analysed (vastus lateralis, deltoids, biceps and triceps brachii), to the training protocol and to the possible intake of anabolic compounds. Regarding myosin isoforms expression and fibre type distribution, many reports have suggested that RT causes a 2X to 2A shift, [77][78][79][80] and this was confirmed in a BB population by Kesidis and colleagues, 81 who found increased percentages of 2A and 1-2A fibres, with lower 2X fibres percentage in BB compared to CTRL. Our results were in agreement, as the proportion of fibres expressing 2A myosin was significantly higher in BB compared to CTRL, at expenses of both 2X fibres and slow fibres. ...
... Antrenman boyunca sürekli bu kas lifi tipini aktifleştirince bu durum Tip IIa ve TipIIb kas lifi tiplerindeki geçişlere öncülük eder. İlginç olarak antrenmansızlık Tip IIb liflerinde artışa, Tip IIa liflerinde ise azalmaya neden olabilmektedir (Andersen, & Aagaard, 2000). Bilim adamları kas lifi tiplerindeki geçişin sadece aynı tip kas lifinde geçerli olabileceğini düşünmektedir. ...
... Ayant un métabolisme oxydatif et étant plus résistante à la fatigue, elles permettent de mobiliser des charges plus longtemps. Par contre, lors d'entrainements en force à charge lourde (> 65 % de 1RM), les fibres de type II semblent préférentiellement s'hypertrophier pour les sujets novices (Volek et coll., 1999 ;Andersen et Aagaard, 2000) tandis que pour les sujets entrainés les différences d'adaptation entre les deux principaux types de fibres ne semblent pas aussi nettes (Häkkinen et coll., 1987). Bien que le principe de taille décrive la relation entre l'intensité de la charge et l'activation musculaire, il est important de prendre également en compte la vitesse d'installation de la force qui peut également influencer le recrutement des UMs. ...
Une nouvelle méthode de musculation, appelée méthode 3/7, consistant à réaliser 5 séries en escalier (de 3 à 7 répétitions) avec une charge de 70 % d’une répétition maximale (1RM) espacées d’un temps de récupération court (15 secondes) s’avère plus efficace pour augmenter la force musculaire qu’une méthode classique (à nombre de répétitions constant) avec un temps de récupération long (150 secondes ; Laurent et coll., 2016). L’intérêt de cette méthode est de combiner l’utilisation de charges modérées tout en induisant une réponse métabolique importante (Penzer et coll., 2016). Au regard du gain de temps que procure cette méthode, elle pourrait être intégrée dans la préparation physique de sportifs, mais également de personnes prises en charge dans le cadre d’une revalidation.Dès lors, l’objectif général de ce travail de thèse a été d’étudier l’efficacité de la méthode 3/7 sur les gains de force et sur les adaptations musculaires et plus spécifiquement de mieux comprendre les facteurs responsables de celle-ci. A cet effet, trois principaux projets ont été élaborés. Le premier avait pour objectif d’optimiser l’efficacité de la méthode 3/7 en investiguant les gains de force maximale, ainsi que les adaptations neurophysiologiques et musculaires sous-jacentes suite à 12 semaines d’entrainement des muscles fléchisseurs du coude. Lors du deuxième projet, l’effet aigu de la méthode 3/7 sur les dommages musculaires, les réponses inflammatoires, hormonales, et métaboliques y compris celles sur le stress oxydant a été évalué à la suite d’une séance de renforcement musculaire composée de quatre exercices (le développé couché, l’extension de jambes à la presse inclinée, le tirage horizontal et la flexion plantaire). Enfin, le troisième projet a permis de suivre l’évolution des réponses biochimiques aigües, des adaptations musculaires et des adaptations nerveuses, ainsi que de la force suite à cette méthode au cours de 22 séances d’entrainement composées des mêmes exercices que ceux du projet 2. Lors de nos 3 projets, la méthode 3/7 a toujours été comparée à une méthode dite classique à charge constante et de volume de travail total similaire mais avec une récupération plus longue (méthode 8x6).Les gains de force maximale ont été déterminés par des contractions volontaires maximales isométriques (CVMI) et la charge maximale mobilisée, lors de 1RM ou de 3RM. L’évolution des paramètres neurophysiologiques a principalement été étudiée par l’activité électromyographique (EMG), l’onde motrice maximale (Mmax) ainsi que le niveau d’activation volontaire maximale (AV). Pour les paramètres biochimiques, nous avons réalisé des analyses des marqueurs sanguins du stress oxydant, du stress métabolique, des dommages musculaires, de la réponse inflammatoire et de la réponse hormonale. Enfin, pour les paramètres musculaires, des mesures échographiques ont été effectuées, et l’évaluation de la masse maigre et de la masse grasse a été déterminée par absorption bi-photonique à rayons X. De plus, le niveau d’oxygénation tissulaire a été mesuré via spectrométrie proche de l’infrarouge.La méthode 3/7 a induit un déficit d’oxygénation plus important que la méthode 8x6 (Projet 1) entrainant une augmentation de lactate et de testostérone dans le sang immédiatement après la séance tandis que les témoins des dommages musculaires (créatine kinase et myoglobine) ont augmenté de manière similaire suite aux 2 méthodes (Projet 2 et 3). Le lactate agirait sur la production d’espèces oxygénées activées (EOA), d’interleukine-6, de cortisol et de l’hormone de croissance qui induiraient à leur tour une augmentation des leucocytes (Projets 2 et 3). La méthode 3/7 a amélioré l’AV sans différence avec la méthode 8x6 (Projet 3) mais a aussi entrainé des adaptations musculaires et amélioré la force maximale (Projet 1 et 3) même si cette méthode n’est pas systématiquement plus efficace que la méthode 8x6 (Projet 3). Il est également à noter que la capacité du sujet à pouvoir réaliser seul le volume de travail imposé par la méthode 3/7 influencerait les adaptations à l’entrainement (Projet 3).Il convient de souligner que l’évolution des paramètres biochimiques n’implique pas une relation directe de cause à effet sur les adaptations musculaires. De plus, le stress métabolique lors de la méthode 3/7 ne semble pas induire systématiquement un effet supplémentaire à la signalisation intramusculaire d’origine mécanique. La synthèse protéique myofibrillaire pourrait atteindre un niveau de saturation de la réponse anabolique suite à la signalisation intramusculaire d’origine mécanique. D’autre part, les divergences des résultats entre nos différents projets pourraient provenir des variabilités inter-individuelles. Les facteurs individuels intrinsèques seraient des déterminants plus importants pour développer la masse musculaire que les paramètres extrinsèques d’un programme d’entrainement. En conclusion, la méthode 3/7 induit des adaptations similaires ou plus importantes qu’une méthode classique (méthode 8x6) mais avec une durée d’entrainement 3 à 4 fois moindre.
... Certaines études récentes ont d'ailleurs retrouvé une diminution d'enzymes glycolytiques, associée à une diminution de l'expression d'isoformes rapides de certaines protéines contractiles et structurelles après entraînement EXC dynamique chez la souris et chez l'humain, suggérant une réorientation vers un métabolisme plus oxydatif (Hody et al., 2011(Hody et al., , 2013. Les fibres musculaires rapides, plus vulnérables à l'exercice EXC, seraient l'objet de modifications plus importantes que les fibres lentes dans les suites d'un exercice EXC, avec une réponse adaptative du muscle qui serait associée à une réorientation des fibres de type IIx vers IIa (augmentation de la proportion des fibres I et IIa par rapport à IIx) (Andersen and Aagaard, 2000;Douglas et al., 2016b;Hody et al., 2013). Concernant l'utilisation des substrats énergétiques pendant l'exercice, l'oxydation des lipides serait majorée pendant un exercice EXC versus CONC de même puissance mécanique. ...
RESUME Le traitement de l'obésité de l'adolescent repose sur des interventions multidisciplinaires associant activité physique et éducation nutritionnelle. Dans un objectif d'amélioration des prises en charge, les recherches cliniques tentent d'identifier les meilleures stratégies à intégrer au sein des programmes d'activité physique. L'entraînement dynamique excentrique (EXC) n'avait jamais été évalué jusqu'ici dans le cadre de l'obésité. La modalité de contraction EXC, qui génère un travail en allongement du muscle, est caractérisée par une grande puissance mécanique développée pour un faible coût métabolique (V ̇ O2). Nous avons fait l'hypothèse que l'entraînement EXC induisait une réduction majorée de la masse grasse en comparaison à l'entraînement classique concentrique (CONC). Chez l'adolescent obèse, les 2 modalités d'entraînement ont été évaluées à même consommation d'oxygène (V ̇ O2), à partir d'un modèle de pédalage sur ergocycle EXC versus CONC. La diminution d'IMC était similaire pour les 2 types d'intervention. En revanche, les bénéfices sur la masse grasse étaient supérieurs après entraînement EXC. De plus, l'entraînement EXC était plus efficace sur le gain de masse et de force musculaire, ainsi que sur la diminution d'insulinorésistance et l'amélioration de la qualité de vie. L'augmentation de la densité minérale osseuse était similaire pour les 2 modalités d'entraînement. Par ailleurs, l'entraînement EXC prévenait l'augmentation de la prise alimentaire observée en réponse aux prises en charge classiques. En complément, l'étude menée sur modèle murin a permis d'évaluer l'impact de l'entraînement EXC, en comparaison à l'entraînement CONC, non seulement à même V ̇ O2 mais également à même puissance mécanique (mais V ̇ O2 moindre en EXC), à partir d'un modèle de course en descente versus montée. Les résultats étaient concordants avec ceux retrouvés chez l'humain et démontraient en particulier que des gains favorables de composition corporelle pouvaient être obtenus en réalisant une activité physique EXC de faible demande métabolique. Ces résultats apparaissent prometteurs pour la mise en place de nouvelles stratégies à intégrer aux programmes de prise en charge de l'obésité. SUMMARY The treatment of paediatric obesity relies on multidisciplinary interventions, focusing on the association of physical activity and nutritional education. Physical activity researches attempt to identify the best strategies in order to improve the management of obesity. No study had evaluated the impact of moderate load eccentric (ECC) training in subjects with obesity yet. ECC exercise is characterized by a lower metabolic demand for a high level of exerted force. We hypothesized that an ECC training would prove more efficient at reducing FM than a classic concentric (CON) training. The first study, carried out on adolescents with obesity, compared ECC training with CON training performed at the same oxygen consumption (V ̇ O2), using a model of ECC training based on ECC versus CON cycling ergometers. The decrease in BMI was similar after the 2 types of training. However, greater adiposity reduction was observed in response to ECC training. Moreover, ECC training bore additional effects on muscle mass, muscle strength, insulin resistance and quality of life. ECC and CON trainings induced a similar increase in bone mineral density. Besides, ECC training might help to prevent the increase in energy intake observed after classical trainings. In addition, the second study carried out on young rats, compared ECC training with CON training with conditions of iso-V ̇ O2 and iso-power output (but lower V ̇ O2 in ECC). ECC training was based on a model of downhill versus uphill running. The results were concordant with the previous described and highlighted that beneficial gains in body composition could be obtained with iso-power but lower V ̇ O2 ECC training. These results appear to be promising in implementing new strategies based on the use of ECC in the management of obesity.
Successful performances in rugby league require the ability to engage in repeated contact efforts with minimal recovery while maintaining a high running intensity. The capacity to express high levels of time-limited force appears to underlie many important physical attributes required to meet the repeated-effort demands of rugby league play. If appropriately periodised and integrated into the training plan, resistance exercise that sufficiently loads the eccentric phase of movement may provide a beneficial stimulus to improve players' force-generating capacity. Comprehensive reviews relating to the adaptive effects of eccentric training and the methods most commonly prescribed in practical environments are available and may provide context for applying these strategies. However, no literature to date has specifically discussed the planning and programming of eccentric resistance exercise to enhance force production characteristics in elite athletes. Therefore, this narrative review focuses on the periodisation of eccentrically-integrated resistance training during a 17-week National Rugby League pre-season phase. To help guide programming during the pre-season period, the 17-week timeline is divided into several phases (i.e., general preparation, special preparation, active rest, and pre-competition). Within the periodised model, eccentric exercise parameters (i.e., volume, load [% 1RM]) are manipulated to progressively increase the rate of muscle lengthening velocity over the pre-season phase and sequentially elicit changes in muscle-tendon properties and neural function that culminate in improving muscular strength expression.
Muscle atrophy is a major health problem that needs effective prevention and treatment approaches. Chronic exercise, an effective treatment strategy for atrophy, promotes muscle hypertrophy, which leads to dynamic metabolic changes; however, the metabolic changes vary among myofiber types. To investigate local metabolic changes due to chronic exercise, we utilized comprehensive proteome and mass spectrometry (MS) imaging analyses. Our training model exhibited hypertrophic features only in glycolytic myofibers. The proteome analyses demonstrated that exercise promoted anabolic pathways, such as protein synthesis, and significant changes in lipid metabolism, but not in glucose metabolism. Furthermore, the fundamental energy sources, glycogen, neutral lipids, and ATP, were sensitive to exercise, and the changes in these sources differed between glycolytic and oxidative myofibers. MS imaging revealed that the lipid composition differs among myofibers; arachidonic acid might be an effective target for promoting lipid metabolism during muscle hypertrophy in oxidative myofibers.
PURPOSE: This study tested the hypothesis that previous strength training episodes favorably contribute to muscular hypertrophic adaptations in rat soleus muscle after long-term detraining and retraining in rats.METHODS: Female Sprague-Dawley rats (n=24) aged 8 weeks were randomly assigned to four groups: control (CON), detraining (DT), strength training (ST), and retraining (RT). The strength training was a regular bout of ladder climbing exercise that consisted of three sets of five repetitions and three days per week for eight weeks. A cylinder containing weights was loaded to the bottom of each rat’s tail. The weights carried during each training session were initially 50% of body weight and progressively increased by 10% per session. Rats in the DT underwent twenty weeks of detraining periods immediately after eight weeks of strength training. Rats in the ST were aged matched to the RT group and underwent eight weeks of strength training at the same duration with the RT group. Rats in the RT were conducted to the resistance training for eight weeks following the detraining period. Soleus muscles were collected at the end of the training episodes to examine alterations in cross-sectional area and protein contents.RESULTS: ST showed a significant increase in cross-sectional area of the rat soleus muscle, compared with CON. It was interestingly demonstrated that RT markedly elicited hypertrophy of soleus muscle, compared with all other groups. It was supported that RTinduced hypertrophy was related to increased myofibrillar protein contents of the soleus muscle.CONCLUSIONS: These results suggest that although prolonged training cessation occurs previous strength training episodes have a positive impact on restoring muscular contractile properties and hypertrophy after retraining.
Muscle fiber size and oxidative metabolism are inversely related, suggesting that a glycolytic metabolism may offer a growth advantage in muscle fibers. However, the mechanisms underlying this advantage remains unknown. Nearly 100 years ago, Warburg reported that cancer cells take up more glucose to produce glycolytic intermediates for anabolic reactions such as amino acid-protein synthesis. The aim of this study was to test whether glycolysis contributes to anabolic signalling responses and hypertrophy in post-mitotic muscle cells. Skeletal muscle hypertrophy was induced in vitro by treating mouse C2C12 myotubes with IGF-1. ¹⁴ C glucose was added to differentiation medium and radioactivity in isolated protein was measured. We exposed differentiated C2C12 and primary mouse myotubes, to 2-deoxyglucose (2DG) and PHGDH siRNA upon which we assessed myotube diameter and signaling pathways involved in the regulation of muscle fiber size. Here, we present evidence that, hypertrophying C2C12 myotubes undergo a cancer-like metabolic reprogramming. First, IGF-1-induced C2C12 myotube hypertrophy increases shunting of carbon from glucose into protein. Second, reduction of glycolysis through 2-deoxy-D-glucose (2DG) lowers C2C12 and primary myotube size 16-40%. Third, reducing the cancer metabolism-associated enzyme PHGDH decreases C2C12 and primary myotube size 25-52%, whereas PHGDH overexpression increases C2C12 myotube size ≈20%. Fourth, the muscle hypertrophy-promoting kinase AKT regulates PHGDH expression. Together these results suggest that glycolysis is important for hypertrophying C2C12 myotubes by reprograming their metabolism similar to cancer cells.
Introduction: Up to 20% of patients undergoing total knee replacement (TKR) surgery report no or suboptimal pain relief after TKR. Moreover, despite chances of recovering to preoperative functional levels, patients receiving TKR have demonstrated persistent deficits in quadriceps strength and functional performance compared with healthy age-matched adults. We intend to examine if low-load blood flow restricted exercise (BFRE) is an effective preoperative method to increase functional capacity, lower limb muscle strength and self-reported outcomes after TKR. In addition, the study aims to investigate to which extent preoperative BFRE will protect against surgery-related atrophy 3 months after TKR.
Methods: In this multicentre, randomised controlled and assessor blinded trial, 84 patients scheduled for TKR will be randomised to receive usual care and 8 weeks of preoperative BFRE or to follow usual care-only. Data will be collected before randomisation, 3-4 days prior to TKR, 6 weeks, 3 months and 12 months after TKR. Primary outcome will be the change in 30 s chair stand test from baseline to 3-month follow-up. Key secondary outcomes will be timed up and go, 40 me fast-paced walk test, isometric knee extensor and flexor strength, patient-reported outcome and selected myofiber properties.Intention-to-treat principle and per-protocol analyses will be conducted. A one-way analysis of variance model will be used to analyse between group mean changes. Preintervention-to-postintervention comparisons will be analysed using a mixed linear model. Also, paired Student's t-test will be performed to gain insight into the potential pretraining-to-post-training differences within the respective training or control groups and regression analysis will be used for analysation of associations between selected outcomes.
Ethical approval: The trial has been accepted by the Central Denmark Region Committee on Biomedical Research Ethics (Journal No 10-72-19-19) and the Danish Data Protection Agency (Journal No 652164). All results will be published in international peer-reviewed scientific journals regardless of positive, negative or inconclusive results.
Background
The aim of the current study was to examine different features of the rectus abdominis muscle (RA) in patients with and without a midline incisional hernia to characterize the effects of a hernia on abdominal wall skeletal muscle.
Material and methods
RA tissue from patients undergoing surgical repair of a large midline incisional hernia (n = 18) was compared with that from an intact abdominal wall in patients undergoing colorectal resection for benign or low-grade malignant disease (n = 18). In addition, needle biopsies were obtained from the vastus lateralis muscle (VL) of all subjects. Outcome measures were muscle fiber type and size, preoperative truncal flexion strength and leg extension power measured in strength-measure equipment, and RA cross-sectional area measured by computed tomography.
Results
In both the RA and VL, the fiber cross-sectional area was greater in the patients with a hernia. The RA cross-sectional area correlated significantly with the truncal flexion strength (r = 0.44, P = 0.015). Patients in the hernia group had a significantly reduced ratio between truncal flexion strength and RA cross-sectional area compared with the control group (41.3 ± 11.5 N/cm²versus 51.2 ± 16.3 N/cm², P = 0.034).
Conclusions
Anatomical displacement of the RA and lack of medial insertion in the linea alba rather than dysfunction secondary to alteration of muscle fiber structure may contribute to impairment of abdominal wall function in patients with midline incisional hernias.
The study was registered at http://www.clinicaltrials.gov/(NCT02011048).
Six women who had participated in a previous 20-wk strength training study for the lower limb detrained for 30-32 wk and subsequently retrained for 6 wk. Seven untrained women also participated in the 6-wk "retraining" phase. In addition, four women from each group volunteered to continue training an additional 7 wk. The initial 20-wk training program caused an increase in maximal dynamic strength, hypertrophy of all three major fiber types, and a decrease in the percentage of type IIb fibers. Detraining had relatively little effect on fiber cross-sectional area but resulted in an increased percentage of type IIb fibers with a concomitant decrease in IIa fibers. Maximal dynamic strength decreased but not to pretraining levels. Retraining for 6 wk resulted in significant increases in the cross-sectional areas of both fast fiber types (IIa and IIab + IIb) compared with detraining values and a decrease in the percentage of type IIb fibers. The 7-wk extension accentuated these trends such that cross-sectional areas continued to increase (nonsignificant) and no IIb fibers could be found. Similar results were found for the nonpreviously trained women. These data suggest that rapid muscular adaptations occur as a result of strength training in previously trained as well as non-previously trained women. Some adaptations (fiber area and maximal dynamic strength) may be retained for long periods during detraining and may contribute to a rapid return to "competitive" form.
The purpose of the present study was to investigate the effects of 8 months of a specific and controlled sprint training programme on three groups of young athletes (two groups of males and one of females). Biopsies of vastus lateralis were taken before and after the period of training. The type percentage and diameter of the fibres, as well as the glycogen content and the activities of the enzymes of glycogen metabolism (glycogen synthase and glycogen phosphorylase), glycolysis (phosphofructokinase, pyruvate kinase, aldolase and lactate dehydrogenase), oxidative metabolism (succinate dehydrogenase) and creatine kinase and aminotransferases were studied. The results show an increase in the percentage of type I fibres and an increase in the diameter of both fibre types. A significant increase was also observed in glycogen content, and in the activities of glycogen synthase, glycogen phosphorylase, phosphofructokinase, pyruvate kinase, succinate dehydrogenase, aspartate aminotransferase and alanine aminotransferase. We conclude that a long period of sprint training induces a biochemical muscle adaptation to anaerobic exercise. This metabolic adaptation is followed by a morphological adaptation, although this is probably not as specific as the biochemical one.
Six sedentary students, six orienteers, and six soccer players were each subjected to 15 tests, comprising 120 s of repeated, maximal isokinetic knee extensions. The tests differed with respect to movement velocity (30 degrees.s-1, 120 degrees.s-1, and 300 degrees.s-1), and movement frequency (5 at each velocity). At a certain velocity, a rectilinear relationship was found between muscular performance intensity (expressed either as average power output or as exercise time ratio) and development of fatigue (expressed either as an absolute or as a fractional decline in work output). Significant inter-velocity differences existed between the slopes of these lines at some combinations of performance and fatigue expressions. Only tendencies towards a difference in x-intercept values were found. This x-intercept value can be taken as a measure of the greatest attainable intensity level of performance without the development of fatigue. This suggestion is valuable both in basic physiological research, and as a possible criterion for optimization of muscular performance. At a given exercise time ratio, increasing movement velocity produced increasing fatigue. However, at a given muscular power output--above 15 W approximately--fatigue developed to a greater extent at the low velocity than at the two higher ones, which did not differ significantly. Substantial individual variation was seen in the positions of the low-, medium-, and high-velocity lines. These variations did not depend on the training background. This implies that the validity of using single-velocity, single-frequency tests in determining isokinetic endurance is doubtful.
We have compared the capillary density and muscle fiber type of musculus vastus lateralis with in vivo insulin action determined by the euglycemic clamp (M value) in 23 Caucasians and 41 Pima Indian nondiabetic men. M value was significantly correlated with capillary density (r = 0.63; P less than or equal to 0.0001), percent type I fibers (r = 0.29; P less than 0.02), and percent type 2B fibers (r = -0.38; P less than 0.003). Fasting plasma glucose and insulin concentrations were significantly negatively correlated with capillary density (r = -0.46, P less than or equal to 0.0001; r = -0.47, P less than or equal to 0.0001, respectively). Waist circumference/thigh circumference ratio was correlated with percent type 1 fibers (r = -0.39; P less than 0.002). These results suggest that diffusion distance from capillary to muscle cells or some associated biochemical change, and fiber type, could play a role in determining in vivo insulin action. The association of muscle fiber type with body fat distribution may indicate that central obesity is only one aspect of a more generalized metabolic syndrome. The data may provide at least a partial explanation for the insulin resistance associated with obesity and for the altered kinetics of insulin action in the obese.
The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical characteristics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.
The growth of one smooth and three individual striated muscles was studied from birth to old age (105 weeks), and where possible during the later stages of foetal life also. Developmental changes in protein turnover (measured in vivo) were related to the changing patterns of growth within each muscle, and the body as a whole. Developmental growth (i.e. protein accumulation) in all muscles involved an increasing proportion of protein per unit wet weight, as well as cellular hypertrophy. The contribution of the heart towards whole-body protein and nucleic acid contents progressively decreased from 18 days of gestation to senility. In contrast, post-natal changes in both slow-twitch (soleus) and fast-twitch (tibialis anterior) skeletal muscles remained reasonably constant with respect to whole-body values. Such age-related growth in all four muscle types was accompanied by a progressive decline in both the fractional rates of protein synthesis and breakdown, the changes in synthesis being more pronounced. Age for age, the fractional rates of synthesis were highest in the oesophageal smooth muscle, similar in both cardiac and the slow-twitch muscles, and lowest in the fast-twitch tibialis muscle. Despite these differences, the developmental fall in synthetic rates was remarkably similar in all four muscles, e.g. the rates at 105 weeks were 30-35% of their values at weaning. Such developmental changes in synthesis were largely related to diminishing ribosomal capacities within each muscle. When measured under near-steady-state conditions (i.e. 105 weeks of age), the half-lives of mixed muscle proteins were 5.1, 10.4, 12.1 and 18.3 days for the smooth, cardiac, soleus and tibialis muscles respectively. Old-age atrophy was evident in the senile animals, this being more marked in each of the four muscle types than in the animal as a whole. In each muscle of the senile rats the protein content and composition per unit wet weight, and both the fractional and total rates of synthesis, were significantly lower than in the muscles of younger, mature, animals (i.e. 44 weeks). In the soleus the decreased synthesis rate appeared to be related to a further fall in the ribosomal capacity. In contrast, the changes in synthesis in the three remaining muscles correlated with significant decreases in the synthetic rate per ribosome.(ABSTRACT TRUNCATED AT 400 WORDS)
Measurement of rates of synthesis of skeletal-muscle proteins in adult rats shows that the faster overall rate of turnover in diaphragm and soleus muscles compared with several other, more glycolytic, muscles is also exhibited by the myofibrillar proteins, since the ratio of sarcoplasmic to myofibrillar protein synthesis is similar for all muscles. Further, throughout postnatal development, when the overall turnover rate falls with age, parallel changes occur for the myofibrillar proteins, as indicated by a constant ratio of sarcoplasmic to myofibrillar protein synthesis (2.06) in the steady state after overnight starvation. Only in the youngest (4 weeks old) rats is a slightly lower ratio observed (1.72). These results indicate that, when changes in the overall turnover rate of muscle proteins occur, the relative turnover of the two major protein fractions stays constant. However, measurements in the non-steady state during growth and after starvation for 4 days show that the relative synthesis rates of the two fractions change as a result of a disproportionate increase in myofibrillar protein synthesis during growth and decrease during starvation. Thus the synthesis rate of the slower-turning-over myofibrillar protein fraction is more sensitive to nutritional state than is that of the sarcoplasmic protein. It is suggested that such responses may help to maintain constant tissue composition during non-steady-state conditions of growth and atrophy.
In order to determine the total number of fibres and the extent to which the relative occurrence of different fibre types varies within m. vastus lateralis, 15 micrometers thick cross-sections of whole muscles were prepared. The total number of type 1 and type 2 fibres was determined in every 48th square millimetre of the section, and the results thus obtained were analysed using a computer program allowing an assessment of bivariate data in the form of contour plots. The total number of fibres varied both in proximal to distal direction in the same muscle and between individuals. No obvious correlation existed between the mean fibre area and the muscle cross-sectional area. The proportion of type 1 fibres in the whole muscle varied between individuals (from 44% to 57%) with a mean value for all five of 52%. The distribution of different fibre types varied within the muscle, mainly as a function of depth, with a predominance to type 2 fibres at the surface and type 1 fibres in deeper regions of the muscle. Thus, the fibre type distribution in m. vastus lateralis is not random. This must be taken into consideration when data on fibre type composition are compared with functional variables.
Several members of the sarcomeric myosin heavy chain (MHC) gene family have been mapped in the human genome but many of them have not yet been identified. In this study we report the identification of two human skeletal MHC genes as fast IIa and IIx MHC based on pattern of expression and sequence homology with the corresponding rat genes in the 3'-translated and untranslated regions. The distribution of these two gene products as well as that of the beta/slow MHC gene was analyzed in human skeletal muscles by in situ hybridization. The distribution of beta/slow, IIa, and IIx MHC transcripts defines three major muscle fiber types expressing a single MHC mRNA, i.e., either beta/slow, IIa, or IIx MHC mRNA, and two populations of hybrid fibers coexpressing beta/slow with IIa or IIa with IIx MHC mRNA. Fiber typing by ATPase histochemistry shows that IIa MHC transcripts are more abundant in histochemical type IIa fibers, whereas IIx MHC transcripts are more abundant in histochemical type IIb fibers.
An 8-wk progressive resistance training program for the lower extremity was performed twice a week to investigate the time course for skeletal muscle adaptations in men and women. Maximal dynamic strength was tested biweekly. Muscle biopsies were extracted at the beginning and every 2 wk of the study from resistance-trained and from nontrained (control) subjects. The muscle samples were analyzed for fiber type composition, cross-sectional area, and myosin heavy chain content. In addition, fasting blood samples were measured for resting serum levels of testosterone, cortisol, and growth hormone. With the exception of the leg press for women (after 2 wk of training) and leg extension for men (after 6 wk of training), absolute and relative maximal dynamic strength was significantly increased after 4 wk of training for all three exercises (squat, leg press, and leg extension) in both sexes. Resistance training also caused a significant decrease in the percentage of type IIb fibers after 2 wk in women and 4 wk in men, an increase in the resting levels of serum testosterone after 4 wk in men, and a decrease in cortisol after 6 wk in men. No significant changes occurred over time for any of the other measured parameters for either sex. These data suggest that skeletal muscle adaptations that may contribute to strength gains of the lower extremity are similar for men and women during the early phase of resistance training and, with the exception of changes in the fast fiber type composition, that they occur gradually.
The effects of 7 weeks of sprint training (repeated 5-s all-out sprints) on maximal power output (W
ν, max) determined during a force-velocity test and a 30-s Wingate test (W
peak) were studied in ten students [22 (SD 2) years] exercising on a cycle ergometer. Before and after training, muscle biopsies were taken from vastus lateralis muscle at rest for the ten subjects and immediately after a training session for five of them. Sprint training induced an improvement both in peak performances by 25% (W
ν, max and W
peak) and in the 30-s total work by 16%. Before sprint training, the velocity reached with no load (ν0) was related to the resting muscle phosphocreatine (PCr) stores (r=0.87, P < 0.001). The training-induced changes in ν0 were observed only when these PCr stores were lowest. This pointed to a possible limiting role of low PCr concentrations in the ability to reach a high velocity. The improvement in performances was linked to an increase in the energy production from anaerobic glycolysis. This result was suggested in muscle by the increase in lactate production measured after a training session associated with the 20% higher activity of both phosphofructokinase and lactate dehydrogenase. The sprint training also increased the proportion of slow twitch fibres closely related to the decrease in fast twitch b fibres. This result would appear to demonstrate an appropriate adaptive reaction following high-intensity intermittent training for the slow twitch fibres which exhibit a greater oxidative capacity.
1. A large population (n = 151) of human skinned skeletal muscle fibres has been studied. Force-velocity curves of sixty-seven fibres were obtained by load-clamp manoeuvres at 12 degrees C. In each fibre maximum shortening velocity (Vmax), maximum power output (Wmax), optimal velocity (velocity at which Wmax is developed, Vopt), optimal force (force at which Wmax is developed, Popt), specific tension (Po/CSA, isometric tension/cross-sectional area) were assessed. Unloaded shortening velocity (Vo) was also determined at 12 degrees C in a different group (n = 57) of fibres by slack-test procedure. 2. All fibres used for mechanical experiments were characterized on the basis of the myosin heavy chain (MHC) isoform composition by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis and divided into five types: type I (or slow), types IIA and IIB (or fast), and types I-IIA and IIA-IIB (or mixed types). 3. Vmax, Wmax, Vopt, Popt, Vopt/Vmax ratio, Po/CSA and Vo were found to depend on MHC isoform composition. All parameters were significantly lower in type I than in the fast (type IIA and IIB) fibres. Among fast fibres, Vmax, Wmax, Vopt and Vo were significantly lower in type IIA and than in IIB fibres, whereas Popt, Po/CSA and Vopt/Vmax were similar. 4. The temperature dependence of Vo and Po/CSA was assessed in a group of twenty-one fibres in the range 12-22 degrees C. In a set of six fibres temperature dependence of Vmax was also studied. The Q10 (5.88) and activation energy E (125 kJ mol-1) values for maximum shortening velocity calculated from Arrhenius plots pointed to a very high temperature sensitivity. Po/CSA was very temperature dependent in the 12-17 degrees C range, but less dependent between 17 and 22 degrees C.
The classic book on human movement in biomechanics, newly updated. Widely used and referenced, David Winter's Biomechanics and Motor Control of Human Movement is a classic examination of techniques used to measure and analyze all body movements as mechanical systems, including such everyday movements as walking. It fills the gap in human movement science area where modern science and technology are integrated with anatomy, muscle physiology, and electromyography to assess and understand human movement. In light of the explosive growth of the field, this new edition updates and enhances the text with: Expanded coverage of 3D kinematics and kinetics. New materials on biomechanical movement synergies and signal processing, including auto and cross correlation, frequency analysis, analog and digital filtering, and ensemble averaging techniques. Presentation of a wide spectrum of measurement and analysis techniques. Updates to all existing chapters. Basic physical and physiological principles in capsule form for quick reference. An essential resource for researchers and student in kinesiology, bioengineering (rehabilitation engineering), physical education, ergonomics, and physical and occupational therapy, this text will also provide valuable to professionals in orthopedics, muscle physiology, and rehabilitation medicine. In response to many requests, the extensive numerical tables contained in Appendix A: "Kinematic, Kinetic, and Energy Data" can also be found at the following Web site: www.wiley.com/go/biomechanics.
The fatiguability of the quadriceps muscle was investigated in 10 male subjects (25-40 yrs), with inter-individual differences in fibre composition of their vastus lateralis muscles (range 25-65% fast twitch, FT, muscle fibres). Fatiguability was assessed as the decline in maximal force (in % of initial values) with 50 repeated isokinetic knee-extensions at fast angular velocity (3.14 rad/s). Each contraction lasted 0.5 s and the rest periods were about 0.7 s. Every subject was tested on two occasions and the standard deviation for a single determination of fatiguability was 1.4%. The decline in force after 50 contractions was on the average about 45%. The individual values varied, however, and a linear correlation was present between fatiguability and % FT fibres (r = 0.86, p less than 0.01). It was concluded that development of fatigue in human skeletal muscle performing repeated fast dynamic contractions with maximal effort was most marked in muscles with a high proportion FT fibres. This finding was in conformity with earlier results from animal skeletal muscle preparations.
Chronic low-frequency stimulation was used for studying the adaptive potential of rat fast-twitch muscle to increased neuromuscular activity. The sequential exchange of myosin heavy chain isoforms HCIIb with HCIId and HCIIa was studied at the translational level using an in-vivo-labeling technique with [35S]methionine. Alterations in heavy chain isoform synthesis, i.e. a decrease in the labeling of HCIIb concomitant with an enhanced labeling of HCIId/IIa, were detectable already two days after the onset of stimulation. This time course corresponds to the previously observed alterations in the amounts of HCIIb and HCIIa mRNAs. However, significant changes in the relative protein amounts of HCIIb and HCIId/IIa were recorded only after an 8-day stimulation period. This delay at the protein level was interpreted to relate to the slow turnover of HCIIb which was estimated from its decay in long-term stimulated muscles with an approximate value of 14.7 days. Therefore, protein degradation seems to be an important post-translational regulatory step in the remodeling process of the thick filament.
Using electrical stimulation to control force generation and limb immobilization to alter the degree of stretch, we have studied the role of mechanical activity in inducing hypertrophy and in determining fast and slow muscle fibre phenotype. Changes in gene expression were detected by analysing the RNA in hybridization studies employing cDNA probes specific for fast and slow myosin heavy chains and other genes. As a result of overload in the stretched position, the fast contracting tibialis anterior muscle in an adult rabbit is induced to synthesize much new protein and to grow by as much as 30% within a period as short as 4 days. This very rapid hypertrophy was found to be associated with an increase of up to 250% in the RNA content of the muscles and an abrupt change in the species of RNA produced. Both stretch alone and electrical stimulation alone caused repression of the fast-type genes and activation of the slow-type genes. it appears that the fast-type IIB genes are the default genes, but that the skeletal slow genes are expressed as a response to overload and stretch. These findings have implications as far as athletic training and rehabilitation are concerned.
Three different training regimens were performed to study the influence of eccentric muscle actions on skeletal muscle adaptive responses to heavy resistance exercise. Middle-aged males performed the leg press and leg extension exercises two days each week. The resistance was selected to induce failure within six to twelve repetitions of each set. Group CON/ECC (n = 8) performed coupled concentric and eccentric actions while group CON (n = 8) used concentric actions only. They did four or five sets of each exercise. Group CON/CON (n = 10) performed twice as many sets with only concentric actions. Eight subjects did not train and served as controls. Tissue samples were obtained from m. vastus lateralis using the biopsy technique before and after 19 weeks of training, and after four weeks of detraining. Histochemical analyses were performed to assess fibre type composition, fibre area and capillarization. Training increased (P less than 0.05) Type IIA and decreased (P less than 0.05) Type IIB fibre percentage. Only group CON/ECC increased Type I area (14%, P less than 0.05). Type II area increased (P less than 0.05) 32 and 27%, respectively, in groups CON/ECC and CON/CON, but not in group CON. Mean fibre area increased (P less than 0.05) 25 and 20% in groups CON/ECC and CON/CON, respectively. Capillaries per fibre increased (P less than 0.05) equally for Type I and Type II fibres. Capillaries per fibre area for both fibre types, however, increased (P less than 0.05) only in groups CON and CON/CON. The changes in fibre type composition and capillary frequency were manifest after detraining.(ABSTRACT TRUNCATED AT 250 WORDS)
Proportions of slow (type 1) muscle fibres of the vastus lateralis and percentage body fat were measured in 11 healthy sedentary men. The proportion of slow muscle fibres was inversely related to fatness; at least 40% of the variability in fatness may be related to variation in muscle fibre type. Metabolic evidence in 50 men, provided by the respiratory exchange ratio (RER) during cycle ergometry, indicated that fatter men (or, in the subset of 11 men, those with a low proportion of slow muscle fibres) combusted less fat during work at 100 W than did lean men (or those with a high proportion of slow fibres). The effects of fitness and of body size were excluded in the analysis. The evidence supports the hypothesis that muscle fibre type is an aetiological factor for obesity.
The myosin heavy chain (MHC) composition of single fibres from m. biceps brachii of young sedentary men (28 +/- 0.4 years, mean +/- SE, n = 4) and male body builders (25 +/- 2.0 years, n = 4) was analysed with a sensitive one-dimensional electrophoretic technique. Compared with sedentary men, the body builders had a higher proportion of fibres containing only MHC type IIa (36 +/- 4 vs 12 +/- 2%; P less than 0.05), but a lower proportion of fibres with a coexistence of MHC types IIa and IIb (16 +/- 3 vs 34 +/- 2%; P less than 0.05) and nearly no fibres containing only MHC type IIb (1 +/- 1 vs 12 +/- 1%; P less than 0.05). Myofibrillar ATPase histochemistry only demonstrated a trend towards a higher proportion of type IIa fibres (31 +/- 6 vs 25 +/- 6%) and a lower proportion of type IIb fibres (18 +/- 5 vs 26 +/- 6%) within the body builders. These results, therefore, suggest an altered expression of MHC isoforms within histochemical type II fibres of human skeletal muscle with body building. Furthermore, in human skeletal muscle differences in expression of MHC isoforms may not always be reflected in the traditional histochemical classification of types I, IIa, IIb and IIc fibres.
The fundamental mechanism underlying the differing rates of tension development in fast and slow mammalian skeletal muscle is still unknown. Now, in skinned (membrane-permeabilized) single fibers it has been shown that the rate of formation of the strongly bound, force-producing cross-bridge between actin and myosin is calcium-sensitive in both fast and slow fibers and that the rate is markedly greater in fast fibers. The transition rates obtained at high calcium concentrations correlated with myosin isoform content, whereas at low calcium concentrations the thin filament regulatory proteins appeared to modulate the rate of tension development, especially in fast fibers. Fiber type-dependent differences in rates of cross-bridge transitions may account for the characteristic rates of tension development in mammalian fast and slow skeletal muscles.
Twenty-four women completed a 20-week heavy-resistance weight training program for the lower extremity. Workouts were twice a week and consisted of warm-up exercises followed by three sets each of full squats, vertical leg presses, leg extensions, and leg curls. All exercises were performed to failure using 6-8 RM (repetition maximum). Weight training caused a significant increase in maximal isotonic strength (1 RM) for each exercise. After training, there was a decrease in body fat percentage (p less than 0.05), and an increase in lean body mass (p less than 0.05) with no overall change in thigh girth. Biopsies were obtained before and after training from the superficial portion of the vastus lateralis muscle. Sections were prepared for histological and histochemical examination. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were distinguished following routine myofibrillar adenosine triphosphatase histochemistry. Areas were determined for fiber types I, IIA, and IIAB + IIB. The heavy-resistance training resulted in significant hypertrophy of all three groups: I (15%), IIA (45%), and IIAB + IIB (57%). These data are similar to those in men and suggest considerable hypertrophy of all major fiber types is also possible in women if exercise intensity and duration are sufficient. In addition, the training resulted in a significant decrease in the percentage of IIB with a concomitant increase in IIA fibers, suggesting that strength training may lead to fiber conversions.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis was analysed by one-dimensional electrophoresis and immunoblotting in three groups of young men with distinct difference in physical activity patterns. No major co-existence of MHC isoforms was found in the group with some daily physical activity. In the very sedentary group, however, 19 +/- 5% (P less than 0.05) of the fibres exhibited coexistence of MHC type IIa and IIb. Further, in the endurance trained group co-existence of MHC type I and IIa was manifested in 36 +/- 4% (P less than 0.05) of the fibres. Disuse and extreme usage of muscle both give rise to an elevation in co-expression of MHC isoforms in single muscle fibres but of markedly different combination of isoforms.