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Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure

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Abstract

Key points: Performing resistance exercise with heavier loads is often proposed to be necessary for the recruitment of larger motor units and activation of type II muscle fibres, leading to type II fibre hypertrophy. Indirect measures (surface electromyography - EMG) have been used to support this thesis, but we propose that lighter loads lifted to task failure (i.e., volitional fatigue) result in similar activation of type II fibres. In this study we had participants perform resistance exercise to task failure with heavier and lighter loads with both a normal and longer repetition duration (i.e., time under tension). Type I and type II muscle fibre glycogen depletion was determined by neither load nor repetition duration during resistance exercise performed to task failure. Surface EMG amplitude was not related to muscle fibre glycogen depletion or anabolic signalling; however, muscle fibre glycogen depletion and anabolic signalling were related. Performing resistance exercise to task failure, regardless of load lifted or repetition duration, necessitates the activation of type II muscle fibres. Abstract: Heavier loads (>60% of maximal strength) are believed to be necessary during resistance exercise (RE) to activate and stimulate hypertrophy of type II fibres. Support for this proposition comes from observation of higher surface electromyography (EMG) amplitudes during RE when lifting heavier vs. lighter loads. We aimed to determine the effect of RE, to task failure, with heavier versus lighter loads and shorter or longer repetition durations on: EMG-derived variables, muscle fibre activation, and anabolic signalling. Ten recreationally-trained young men performed four unilateral RE conditions randomly on two occasions (two conditions, one per leg per visit). Muscle biopsies were taken from the vastus lateralis before and one hour after RE. Broadly, total time under load, number of repetitions, exercise volume, EMG amplitude (at the beginning and end of each set), and total EMG activity were significantly different between conditions (P < 0.05); however, neither glycogen depletion (in both type I and type II fibres) nor phosphorylation of relevant signalling proteins were different between conditions. We conclude that muscle fibre activation and subsequent anabolic signalling are independent of load, repetition duration, and surface EMG amplitude, when RE is performed to task failure. Our results provide evidence that type I and type II fibres are activated when heavier and lighter loads are lifted to task failure. We propose that our results explain why RE training with higher or lower loads, when loads are lifted to task failure, result in equivalent muscle hypertrophy and occurs in both type I and type II fibres. This article is protected by copyright. All rights reserved.

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... A recent study published in The Journal of Physiology is a timely addition to the literature and provides intriguing information on this topic. Briefly, Morton et al. (2019) demonstrated that both low-load (30% 1RM) and high-load (80% 1RM) lower-body resistance exercise performed to muscle failure results in different effects on time-under-load, training volume and surface electromyography amplitude. Despite these differences, the depletion of muscle glycogen and anabolic signalling were similar in both muscle fibre types regardless of the load used in the exercise session. ...
... Based on the results of this study, it would be tempting to conclude that both low-load and high-load resistance training may, over the long term, produce similar hypertrophic effects on type I and type II muscle fibre hypertrophy. However, we should not disregard that the study by Morton et al. (2019) had an acute design. Even though these findings might hypothetically suggest that hypertrophy of type I and type II muscle fibres would also be the same when training with low and high loads, there is still a need for future long-term studies that would directly answer this question. ...
... In addition to future longitudinal studies, future acute research is needed to explore if there is a minimal threshold of external resistance necessary for eliciting the activation of both muscle fibre types. For example, would the results by Morton et al. (2019) be replicated using even lower loads such as 10% or 20% 1RM? If future acute, as well as long-term studies, confirm that load indeed is not an important determinant of muscle fibre activation and subsequently muscle fibre hypertrophy (provided that sets are carried out to the point of muscle failure), these findings may have considerable value in the prescription of resistance training. ...
... The modest reduction (38%) in the biochemically measured mixed glycogen concentration by 150 mmol/kg are in line with previous reports demonstrating reductions between 100 and 250 mmol/kg using various resistance exercise protocols. [3][4][5][6][7][8][9][10] Interestingly, total training volume seems to be a stronger determinant of the overall glycogen depletion during acute exercise sessions than exercise intensity per se (% of 1RM), 3,19 probably reflecting that a high energy turnover exits for all loading intensities. In the present study, a discrimination between fibre types revealed a slightly higher glycogen use by type 2 fibres than by type 1 fibres (50% vs 30%, respectively). ...
... This is in line with previous reports demonstrating a higher glycogen use in type 2 compared to type 1 fibres. 19,20,21 In the present study, a discrimination between fibre types revealed a slightly higher glycogen use by type 2 fibres than by type 1 fibres (50% vs 30%, respectively). This is in line with previous reports demonstrating a greater depletion of glycogen in type 2 fibres compared to type 1 fibres. ...
... This is in line with previous reports demonstrating a greater depletion of glycogen in type 2 fibres compared to type 1 fibres. 19,20,21 In the present high-intensity resistance exercise session we expected all type 1 fibres and most of the type 2 fibres in the vastus lateralis to be recruited 22 and, therefore, the higher glycogen Submitted version of the accepted manuscript in Acta Physiologica (https://doi.org/10.1111/apha.13561) utilization observed in type 2 fibres is likely to be explained by their more glycolytic, less oxidative phenotype that would require usage of more glycogen for a given amount of work produced. ...
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Aim: Glycogen particles are found in different subcellular localizations, which are utilized heterogeneously in different fibre types during endurance exercise. Although resistance exercise typically involves only a moderate use of mixed muscle glycogen, the hypothesis of the present study was that high-volume heavy-load resistance exercise would mediate a pattern of substantial glycogen depletion in specific subcellular localizations and fibre types. Methods: 10 male elite weightlifters performed resistance exercise consisting of 4 sets of 5 (4x5) repetitions at 75% of 1RM back squats, 4x5 at 75% of 1RM deadlifts and 4x12 at 65% of 1RM rear foot elevated split squats. Muscle biopsies (vastus lateralis) were obtained before and after the exercise session. The volumetric content of intermyofibrillar (between myofibrils), intramyofibrillar (within myofibrils) and subsarcolemmal glycogen was assessed by transmission electron microscopy. Results: After exercise, biochemically determined muscle glycogen decreased by 38 (31:45)%. Location-specific glycogen analyses revealed in type 1 fibres a large decrement in intermyofibrillar glycogen, but no or only minor changes in intramyofibrillar or subsarcolemmal glycogen. In type 2 fibres, large decrements in glycogen were observed in all subcellular localizations. Notably, a substantial fraction of the type 2 fibres demonstrated near-depleted levels of intramyofibrillar glycogen after the exercise session. Conclusion: Heavy resistance exercise mediates a substantial utilization of glycogen from all three subcellular localization in type 2 fibres, while mostly taxing intermyofibrillar glycogen stores in type 1 fibres. Thus, a better understanding of the impact of resistance training on myocellular metabolism and performance requires a focus on compartmentalized glycogen utilization.
... 0.05). On the other hand, a significant main effect of set was observed for concentric peak velocity (F 2, 28 ...
... The comparison of the adaptations provoked by RT conducted under different loading conditions (heavy vs. moderate or light) has received increasing attention during recent years (15,17,26,28). Several studies conducted in young people have demonstrated that moderate-load or light-load RT can induce similar gains in muscle mass and strength as heavy-load RT when mechanical work is similar (5,26). ...
Article
Rodriguez-Lopez, C, Alcazar, J, Sánchez-Martín, C, Ara, I, Csapo, R, and Alegre, LM. Mechanical characteristics in heavy vs. light load ballistic resistance training in older adults. J Strength Cond Res XX(X): 000-000, 2020-Although power-oriented resistance training (RT) is strongly recommended to counter age-related neuromuscular function declines, there is still controversy about which intensities of load should be used to elicit optimal training adaptations. Knowledge of the mechanical characteristics of power-oriented RT performed at different intensities might help to better understand the training stimulus that triggers load-dependent adaptations in older adults. Using a cross-over design, 15 well-functioning older volunteers (9 men and 6 women; 73.6 ± 3.8 years) completed 2 volume × load-matched ballistic RT sessions with heavy (HL: 6 × 6 × 80% 1-repetition maximum [1RM]) and light-load (LL: 6 × 12 × 40% 1RM) on a horizontal leg press exercise. Electromyographic (EMG) and mechanical variables (work, force, velocity, and power) as well as intraset neuromuscular fatigue (i.e., relative losses in force, velocity, and power) were analyzed. More concentric mechanical work was performed in the LL training session, compared with HL (36.2 ± 11.2%; p < 0.001). Despite the higher mean EMG activity of the quadriceps femoris muscle (13.2 ± 21.1%; p = 0.038) and greater concentric force (35.2 ± 7.6%; p < 0.001) during HL, higher concentric velocity (41.0 ± 12.7%, p < 0.001) and a trend toward higher concentric power (7.2 ± 18.9%, p = 0.075) were found for LL. Relative velocity losses were similar in both sessions (≈10%); however, relative force losses were only found in LL (7.4 ± 6.5%, p = 0.003). Considering the greater mechanical work performed and concentric power generated, ballistic RT using LL may, therefore, represent a stronger stimulus driving training adaptations as compared with volume × load-matched heavy-load training. Relative losses in force and power should be monitored in addition to velocity losses during ballistic RT.
... One recent study (30) observed greater MU firing rates and larger action potential amplitudes of the VL during high-intensity contractions (70% maximum voluntary contraction [MVC]) performed to fatigue in comparison to lowintensity contractions (30% MVC) of the leg extensors performed to fatigue. The results indicated that the repetitive 30% MVCs did not necessitate the excitatory drive or recruitment equal to that of the repetitive 70% MVCs before exhaustion was reached, which contrasts what would be predicted by the model (33) and by other researchers suggesting that low-to-moderate-intensity contractions performed to fatigue recruit the entire MU pool (27,29). However, no study has investigated differences in neural drive and MU recruitment between a moderate-intensity contraction performed to fatigue and a single, near maximal, high-intensity contraction. ...
... There may be many measures by which high-intensity contractions are indistinguishable from fatiguing moderate-intensity contractions, but conclusions should not be drawn from these alone. Many studies have reported similarities between fatiguing low-or moderate-intensity and high-intensity resistance training in hormone responses (28), fiber type specific muscle glycogen depletion (29), and one study reported similar peak EMG amplitude (34). In addition, studies have reported similar responses to such training programs for strength (11,16) and muscle hypertrophy, in Type I and Type II fiber cross-sectional area (28) or whole muscle Motor Unit Activity and Contraction Intensity (2020) 00:00 | www.nsca.com ...
... It has been suggested that this is the minimum threshold required to activate the complete range of fiber types, particularly those related with the largest motor units (40). A recent study has shown that low or high loads of resistance exercises to task failure, lead to equivalent type I and type II muscle fiber glycogen depletion regardless of load or repetition duration (33). However, the authors emphasized that the method used in this study may lack sensitivity as an indicator of muscle fiber depolarization and that glycogen is not the only substrate used during fatigue contractions (33). ...
... A recent study has shown that low or high loads of resistance exercises to task failure, lead to equivalent type I and type II muscle fiber glycogen depletion regardless of load or repetition duration (33). However, the authors emphasized that the method used in this study may lack sensitivity as an indicator of muscle fiber depolarization and that glycogen is not the only substrate used during fatigue contractions (33). ...
Article
Effects of blood flow restriction training on muscle strength and architecture. J Strength Cond Res XX(X): 000-000, 2020-The aim of this study was to compare the effect of the traditional resistance (RES) training and low-intensity resistance training with blood flow restriction (BFR) protocols on quadriceps and hamstring muscle strength, and rectus femoris (RF) and vastus lateralis architecture, in youth team soccer players. Twenty-three young trained soccer team players were divided into 2 groups: the RES group that practiced traditional high-intensity resistance training (80% 1 repetition maximum [1RM], 4 sets, 12 rep.) (n = 12) and the BFR group that performed low-intensity resistance exercise with BFR (30% 1RM, 4 sets, 30-15-15-15 rep) (n = 11)-unilateral knee extension exercise-twice a week for 6 weeks. Muscle strength (isokinetic concentric peak torque of the quadriceps and hamstring muscles) and ultrasonographic parameters (muscle thickness, pennation angle, and fascicle length) were assessed. Bilateral knee flexor and extensor strength was increased in both groups compared with pre-exercise. The increase in dominant side extensor muscle strength (60°·s p = 0.02, ηp = 0.256, 180°·s p = 0.019, ηp = 0.271) and RF thickness (p = 0.002, ηp = 0.361) was statistically higher in the BFR group than in the RES group. These findings support that occlusion training can provide better benefits than traditional strength training to improve muscle hypertrophy. In addition, the novelty of our study is that BFR training may affect the muscle structure measured by ultrasonography.
... However, the main point that supports such a line of reasoning is that, when comparing training intensities, high loads and low repetitions vs. low loads and high repetitions exhibit different muscular activations (evaluated by surface electromyography [sEMG]), although both training protocols seem to induce similar muscle growth (24,29,30). A possible justification for this may lie in the method used, i.e., sEMG, which not necessarily correspond to the mechanical stress experienced by the muscle fibers (15,30). Indeed, a previous study showed that when measuring muscular activation using fiber type-specific glycogen depletion obtained by essays of muscle biopsies, high and low load performed until failure elicited similar results (15). ...
... A possible justification for this may lie in the method used, i.e., sEMG, which not necessarily correspond to the mechanical stress experienced by the muscle fibers (15,30). Indeed, a previous study showed that when measuring muscular activation using fiber type-specific glycogen depletion obtained by essays of muscle biopsies, high and low load performed until failure elicited similar results (15). Regardless, the proposed poor relationship between sEMG and hypertrophy responses (29,30), however, possibly cannot be generalized to experimental designs . ...
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The aim of the present study was to compare the changes in gastrocnemius muscle thickness (MT) between conditions in which foot was pointed outward (FPO), inward (FPI), or forward (FPF). Twenty-two young men (23 ± 4 years) were selected and performed a whole-body resistance training program three times per week for nine weeks, with differences in the exercise specific for calves. Calf-raise exercise was performed unilaterally, in a pin-loaded seated horizontal leg-press machine, in 3 sets of 20-25 repetitions for training weeks 1-3, and 4 sets for weeks 4-9. Each subject's leg was randomly assigned for one of the three groups according to foot position: FPO, FPI, and FPF. Measurements with a B-mode ultrasound were performed to assess changes in MT of medial and lateral gastrocnemius heads. After training period, there were observed increases in MT of both medial (FPO = 8.4%; FPI = 3.8%; FPF = 5.8%) and lateral (FPO = 5.5%; FPI = 9.1%; FPF = 6.4%) gastrocnemius, and significant differences for magnitude of the gains were observed between FPO and FPI conditions (P < 0.05). Positioning FPO potentiated the increases in MT of medial gastrocnemius, while FPI provided greater gains for the lateral head. Our results suggest that head-specific muscle hypertrophy may be obtained selectively for gastrocnemius after nine weeks of calf training in young male adults.
... A key question when access to training facilities is limited is whether heavy loads during resistance training are required for the development, or maintenance, of muscle mass and strength. During resistance exercise all motor units are recruited at momentary muscular failure, regardless of the load used [74]. In turn, rates of muscle protein synthesis for up to 24 hours after exercise were similar when healthy men performed knee extension at 30 % of one repetition maximum (1RM) to failure compared with 90 % 1RM to failure [75]. ...
Article
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The COVID-19 pandemic in 2020 has resulted in widespread training disruption in many sports. Some athletes have access to facilities and equipment, while others have limited or no access, severely limiting their training practices. A primary concern is that the maintenance of key physical qualities (e. g. strength, power, high-speed running ability, acceleration, deceleration and change of direction), game-specific contact skills (e. g. tackling) and decision-making ability, are challenged, impacting performance and injury risk on resumption of training and competition. In extended periods of reduced training, without targeted intervention, changes in body composition and function can be profound. However, there are strategies that can dramatically mitigate potential losses, including resistance training to failure with lighter loads, plyometric training, exposure to high-speed running to ensure appropriate hamstring conditioning, and nutritional intervention. Athletes may require psychological support given the challenges associated with isolation and a change in regular training routine. While training restrictions may result in a decrease in some physical and psychological qualities, athletes can return in a positive state following an enforced period of rest and recovery. On return to training, the focus should be on progression of all aspects of training, taking into account the status of individual athletes.
... In fact, changes in RD seem to influence the amplitude of EMG, with shorter RDs resulting in larger EMG amplitudes (Sakamoto & Sinclair, 2012). However, muscle fiber activation and subsequent anabolic signaling are independent of EMG amplitude when resistance exercise is performed to concentric muscle failure (Morton et al., 2019). Additionally, similar muscle strength gains and hypertrophy between RT protocols with different EMG amplitudes has been recently shown (Mitchell et al., 2012;Morton et al., 2016;Nobrega et al., 2018b;Schoenfeld et al., 2014). ...
Article
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The aim of this study was to compare the effect of self-selected repetition duration (SELF), with and without volume load (VL) equalized with controlled repetition duration (CON) on muscle strength and hypertrophy in untrained males. We used a within-subjects design in which 20 volunteers (age: 24.7 ± 2.9 years) had one leg randomly assigned to CON (i.e., 2 s concentric, 2 s eccentric) and the other to SELF or to self-selected repetition duration with equalized volume load (SELF-EV). One repetition maximum (1-RM) and muscle cross-sectional area (CSA) were measured at baseline (Pre) and after (Post) resistance training (RT; 2×/wk for 8 weeks). For the main study variables (1-RM and muscle CSA), a mixed-model analysis was performed, assuming repetition duration (SELF, SELF-EV and CON), and time (Pre and Post) as fixed factors and the subjects as random factor for each dependent variable (1-RM and CSA). All RT protocols showed significant increases in values of 1-RM from Pre (CON: 73.7 ± 17.6 kg; SELF: 75.9 ± 17.7 kg; and SELF-EV: 72.6 ± 16.9 kg) to Post (CON: 83.4 ± 19.9 kg, effect size (ES): 0.47; SELF: 84 ± 19.1 kg, ES: 0.43; and SELF-EV: 83.2 ± 19.9 kg, ES: 0.57, P < 0.0001). Muscle CSA values increased for all protocols from Pre (CON: 12.09 ± 3.14 cm ² ; SELF: 11.91 ± 3.71 cm ² ; and SELF-EV: 11.93 ± 2.32 cm ² ) to Post (CON: 13.03 ± 3.25 cm ² , ES: 0.29; SELF: 13.2 ± 4.16 cm ² , ES: 0.32; and SELF-EV: 13.2 ± 2.35 cm ² , ES: 0.53, P < 0.0001). No significant differences between protocols were found for both 1-RM and CSA ( P > 0.05). Performing RT with SELF, regardless of VL, was equally effective in inducing increases in muscle strength and hypertrophy compared to CON in untrained men.
... Moderateto-higher volume resistance exercise involves performing more repetitions using light to moderate loads (sets consisting of >10 repetitions at ≤65% 1RM). There has been recent enthusiasm surrounding molecular signaling events that occur in skeletal muscle in response to higher load versus moderate-to-higher volume resistance exercise (Burd et al., 2010;Haun et al., 2017;Morton et al., 2019). In general, these studies have reported that acute anabolic signaling events do not differ between exercise modalities when lifts are performed to volitional fatigue. ...
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While high-load resistance training increases muscle hypertrophy, the intramuscular protein responses to this form of training remains largely unknown. In the current study, recreationally resistance-trained college-aged males (N = 15; mean ± SD: 23 ± 3 years old, 6 ± 5 years training) performed full-body, low-volume, high-load [68–90% of one repetition maximum (1RM)] resistance training over 10 weeks. Back squat strength testing, body composition testing, and a vastus lateralis biopsy were performed before (PRE) and 72 h after the 10-week training program (POST). Fiber type-specific cross-sectional area (fCSA), myofibrillar protein concentrations, sarcoplasmic protein concentrations, myosin heavy chain and actin protein abundances, and muscle tissue percent fluid were analyzed. The abundances of individual sarcoplasmic proteins in 10 of the 15 participants were also assessed using proteomics. Significant increases (p < 0.05) in type II fCSA and back squat strength occurred with training, although whole-body fat-free mass paradoxically decreased (p = 0.026). No changes in sarcoplasmic protein concentrations or muscle tissue percent fluid were observed. Myosin heavy chain protein abundance trended downward (−2.9 ± 5.8%, p = 0.069) and actin protein abundance decreased (−3.2 ± 5.3%, p = 0.034) with training. Proteomics indicated only 13 sarcoplasmic proteins were altered with training (12 up-regulated, 1 down-regulated, p < 0.05). Bioinformatics indicated no signaling pathways were affected, and proteins involved with metabolism (e.g., ATP-PCr, glycolysis, TCA cycle, or beta-oxidation) were not affected. These data comprehensively describe intramuscular protein adaptations that occur following 10 weeks of high-load resistance training. Although previous data from our laboratory suggests high-volume resistance training enhances the ATP-PCr and glycolytic pathways, we observed different changes in metabolism-related proteins in the current study with high-load training.
... To compensate for the lower RE load during low-repetitions, highintensity routines (due to the neurological deficit), a possible suggestion is that individuals with CP should instead increase training volume and always aim for repetitions until failure (volitional fatigue). Resistance exercise until failure using >7-10 RM loading, rather than fewer repetitions with high intensity, still calls for both type I and type II muscle fiber activation and produces a similar muscle fiber activation pattern compared with a short duration high-intensity protocol (37). Furthermore, data show that chronic RE training with low loads until failure results in hypertrophy of both type I and type II fibres in TD subjects (38)(39)(40). ...
Article
Introduction: The development of efficient resistance exercise protocols to counteract muscle dysfunction in cerebral palsy is warranted. Whether individuals with cerebral palsy are able to perform iso-inertial resistance (flywheel) exercise in a comparable manner to typically developed subjects has never been experimentally tested. Design: A comparative, controlled study. Subjects: Eight young ambulatory adults with cerebral palsy (mean age 19 years; Gross Motor Function Classification System (GMFCS) I-III) and 8 typically developed control subjects (mean age 21 years). Methods: Subjects performed acute bouts on the weight-stack and flywheel leg-press device, respectively. Range of motion, electromyography, power, work and muscle thickness (ultrasound) data were collected. Results: Subjects with cerebral palsy were able to produce a greater eccentric/concentric peak power ratio on the flywheel (p < 0.05 vs ratio in weight-stack), however absolute values were lower (p < 0.05 vs weight-stack). Typically developed subjects produced more power per mm of thigh muscle than the cerebral palsy group, independent of leg, device and action. Discussion: Subjects with cerebral palsy could not elicit the eccentric overload seen in typically developed subjects. Furthermore, peak power production per mm muscle was markedly reduced in both legs in subjects with cerebral palsy. In conclusion, this comparative study of weight-stack and flywheel exercise does not support the implementation of the current iso-inertial protocol for young adults with cerebral palsy.
... A key question when access to training facilities is limited is whether heavy loads during resistance training are required for the development, or maintenance, of muscle mass and strength. During resistance exercise all motor units are recruited at momentary muscular failure, regardless of the load used [74]. In turn, rates of muscle protein synthesis for up to 24 hours after exercise were similar when healthy men performed knee extension at 30 % of one repetition maximum (1RM) to failure compared with 90 % 1RM to failure [75]. ...
Article
The COVID-19 pandemic in 2020 has resulted in widespread training disruption in many sports. Some athletes have access to facilities and equipment, while others have limited or no access, severely limiting their training practices. A primary concern is that the maintenance of key physical qualities (e. g. strength, power, high-speed running ability, acceleration, deceleration and change of direction), game-specific contact skills (e. g. tackling) and decision-making ability, are challenged, impacting performance and injury risk on resumption of training and competition. In extended periods of reduced training, without targeted intervention, changes in body composition and function can be profound. However, there are strategies that can dramatically mitigate potential losses, including resistance training to failure with lighter loads, plyometric training, exposure to high-speed running to ensure appropriate hamstring conditioning, and nutritional intervention. Athletes may require psychological support given the challenges associated with isolation and a change in regular training routine. While training restrictions may result in a decrease in some physical and psychological qualities, athletes can return in a positive state following an enforced period of rest and recovery. On return to training, the focus should be on progression of all aspects of training, taking into account the status of individual athletes.
... For example, low load (e.g., 30% 1RM) training performed to volitional failure produces similar skeletal muscle growth as traditional high load training (e.g., 70-80% 1RM) (20,27). In addition, acute work has demonstrated that high load and low load training result in similar muscle fiber activation, based on muscle fiber glycogen depletion, when loads are lifted to task failure (23). A review by Ozaki et al. speculates that skeletal muscle growth is achieved through a combination of external load or metabolic induced motor unit recruitment or both (29). ...
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Changes in muscle thickness (MT), isometric torque, and arterial occlusion pressure (AOP) were examined following four sets of twenty unilateral elbow flexion exercise. Participants performed four sets of maximal voluntary contractions with no external load throughout a full range of motion of a bicep curl with and without the application of blood flow restriction (BFR). For torque there was an interaction (p = 0.012). The BFR condition had lower torque following exercise (56.07 ± 17.78 Nm) compared to the control condition (58.67 ± 19.06 Nm). For MT, there was a main effect for time (p < 0.001). MT increased from pre (3.52 ± .78cm) to post (3.68 ± 81cm) exercise and remained increased above baseline 15 min post-exercise. For AOP, there was an interaction (p = 0.027). The change in AOP was greater in the BFR condition (16.6 ± 13.42mmHg) compared to the control (11.1 ± 11.84 mmHg). NO LOAD exercise with BFR let to greater reductions in torque and an exaggerated cardiovascular response compared to exercise alone. There were no differences in swelling. These results suggest that the application of BFR to NO LOAD exercise may result in greater fatigue.
... It is not clear to us what caused such difference in the exercise-induced metabolic stress and myoelectrical activity observed in this study. Interestingly, Morton et al. (2019) observed similar intramuscular glycogen depletion in types I and II muscle fibers following high-load (80% of 1-RM) and lowload (30% of 1-RM) resistance exercise, regardless of greater sEMG amplitude observed during the high-load condition. These findings suggest that activation of the higher threshold type II muscle fiber may occur during low-load resistance exercise without resulting in a greater sEMG amplitude. ...
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This study compared the acute physiological responses of traditional and practical blood flow restriction resistance exercise (tBFR and pBFR, respectively) and high- and low-load resistance exercise without BFR (HL and LL, respectively), as well as the potential sex differences within the aforementioned exercise methods. Fourteen men and fifteen women randomly completed the following experimental conditions: (1) tBFR, consisting of four sets of 30-15-15-15 repetitions of the bilateral horizontal leg press and knee extension exercises, at 30% of one-repetition maximum (1-RM), with a 13.5 cm wide pneumatic cuff placed at the most proximal portion of each thigh and inflated to a pressure equivalent to 50% of the participant’s total occlusion pressure; (2) pBFR, which was the same as the tBFR condition, except that an elastic band wrapped around the proximal portion of each thigh at a tightness of 7 on a 0 to 10 perceived pressure scale was used to reduce blood flow; (3) LL, same as the tBFR and pBFR protocols, except that no BFR was applied; and (4) HL, consisting of 3 sets of 10 repetitions at 80% of 1-RM, with the same 1-min rest interval between sets and a 3-min rest period between exercises. At baseline, immediately post-, 5 min post-, and 15 min post-exercise, whole-blood lactate (WBL), indices of muscle swelling (muscle thickness and thigh circumference), hematocrit and plasma volume changes, were measured as well as superficial electromyography (sEMG) amplitude during exercise. There were no significant (p > 0.05) differences between the tBFR and pBFR exercise protocols for any of the physiological parameters assessed. However, significantly greater (p < 0.05) WBL and sEMG values were observed for HL compared to the remaining exercise conditions. Finally, males displayed greater WBL levels than females at 15 min post-exercise. Interestingly, males also displayed significantly (p < 0.05) greater sEMG amplitude than females within the low-load trials during leg press, but no significant (p < 0.05) sex differences were observed during knee extension. In conclusion, tBFR and pBFR seemed to be capable of inducing the same acute physiological responses. Furthermore, males displayed greater responses than females for some of the physiological parameters measured.
... In humans, the force of a muscle contraction is partly regulated by the number, frequency, and synchronization of the motor units recruited [5,6]. Low threshold motor units are mainly recruited in low intensity exercises, whereas both low and high threshold motor units are recruited during high intensity exercises [6] or low intensity exercises performed to task failure [7]. ...
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The aim of this study was to analyze the literature on muscle activation measured by surface electromyography (sEMG) of the muscles recruited when performing the leg press exercise and its variants. The Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to report this review. The search was carried out using the PubMed, Scopus, and Web of Science electronic databases. The articles selected met the following inclusion criteria: (a) a cross-sectional or longitudinal study design; (b) neuromuscular activation assessed during the leg press exercise, or its variants; (c) muscle activation data collected using sEMG; and (d) study samples comprising healthy and trained participants. The main findings indicate that the leg press exercise elicited the greatest sEMG activity from the quadriceps muscle complex, which was shown to be greater as the knee flexion angle increased. In conclusion, (1) the vastus lateralis and vastus medialis elicited the greatest muscle activation during the leg press exercise, followed closely by the rectus femoris; (2) the biceps femoris and the gastrocnemius medialis showed greater muscular activity as the knee reached full extension, whereas the vastus lateralis and medialis, the rectus femoris, and the tibialis anterior showed a decreasing muscular activity pattern as the knee reached full extension; (3) evidence on the influence of kinematics modifications over sEMG during leg press variants is still not compelling as very few studies match their findings.
... It has been suggested that performing RT to concentric muscle failure (Jenkins et al. 2015;Schoenfeld et al. 2015) can maximize gains in muscle strength (Rooney et al. 1994;Drinkwater et al. 2005) and hypertrophy (Schott et al. 1995), due to the increase in the muscle activation, regardless of training variables manipulation or methods (Souza et al. 2014;Barcelos et al. 2018;Nobrega et al. 2018;Damas et al. 2019;Lasevicius et al. 2019). In fact, it has been recently shown that manipulation of load, time under tension and number of repetitions during RT resulted in similar muscle activation when exercises were performed to concentric muscle failure (Morton et al. 2019). Accordingly, studies comparing the effects of bench press exercise with push-ups performed with body weight, which resembles the ST scheme, showed similar increases in muscle mass and strength when both were performed to concentric muscle failure (Calatayud et al. 2015;Kikuchi and Nakazato 2017). ...
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The study by Jenkins et al. attempted to elucidate the mechanisms behind the findings of Mitchell et al. (J Appl Physiol 113(1):71-77, 2012). However, we believe the work of Jenkins et al. contains methodological issues, does not meet electromyographic reporting standards, and deduces conclusions beyond which can be interpreted from the data provided.
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Quantification of muscle protein synthesis (MPS) remains a cornerstone to understanding the control of muscle mass. Traditional (13)C-amino-acid tracer methodologies necessitate sustained bed-rest and intravenous cannulation(s), restricting studies to ~12h, and thus cannot holistically inform on diurnal MPS. This limits insight into the regulation of habitual muscle metabolism in health, ageing and disease while querying the utility of tracer-techniques to predict the long-term efficacy of anabolic/anti-catabolic interventions. We tested the efficacy of the D2O tracer for quantifying MPS over a period not feasible with (13)C tracers and too short to quantify changes in mass. Eight men (22±3.5y) undertook one-legged resistance-exercise over 8-d (4×8-10 repetitions: 80%-1RM every second-day, to yield 'non-exercised' vs. 'exercise' leg-comparisons) with Vastus Lateralis biopsies taken bi-laterally: 0, 2, 4 and 8-days. After day-0 biopsies, participants consumed a D2O bolus (150ml; 70-Atom%); saliva was collected daily. Fractional synthetic rates (FSR) of myofibrillar (MyoPS), sarcoplasmic (SPS) and collagen (CPS) protein-fractions were measured by GC-Pyrolysis-IRMS and TC/EA-IRMS. Body-water initially enriched at 0.16-0.24 APE, decayed at ~0.009%.d-1. In the non-exercised-leg, MyoPS was: 1.45±0.10%.d-1, 1.47±0.06%.d(-1), 1.35±0.07%.d-1 at 0-2, 0-4 and 0-8d respectively (~0.05-0.06%.h-1). MyoPS was greater in the exercised-leg (0-2d 1.97±0.13%.d(-1), 0-4d 1.96±0.15%.d-1; P<0.01, 0-8d 1.79±0.12%.d(-1); P<0.05). CPS was slower than MyoPS, but followed a similar pattern, with the exercised-leg tending to yield greater FSR's (0-2d; 1.14±0.13%.d-1 vs. 1.45±0.15%.d(-1), 0-4d; 1.13±0.07%.d(-1) vs. 1.47±0.18%.d(-1), 0-8d; 1.03±0.09%.d(-1) vs. 1.40±0.11%.d(-1)). SPS remained unchanged. Therefore, D2O has unrivaled utility to quantify day-to-day MPS in humans and inform on short-term changes in anabolism, and presumably, catabolism alike.
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We determined the effect of muscle glycogen concentration and postexercise nutrition on anabolic signaling and rates of myofibrillar protein synthesis after resistance exercise (REX). Sixteen young, healthy men matched for age, body mass, peak oxygen uptake (Vo(2peak)) and strength (one repetition maximum; 1RM) were randomly assigned to either a nutrient or placebo group. After 48 h diet and exercise control, subjects undertook a glycogen-depletion protocol consisting of one-leg cycling to fatigue (LOW), whereas the other leg rested (NORM). The next morning following an overnight fast, a primed, constant infusion of l-[ring-(13)C(6)] phenylalanine was commenced and subjects completed 8 sets of 5 unilateral leg press repetitions at 80% 1RM. Immediately after REX and 2 h later, subjects consumed a 500 ml bolus of a protein/CHO (20 g whey + 40 g maltodextrin) or placebo beverage. Muscle biopsies from the vastus lateralis of both legs were taken at rest and 1 and 4 h after REX. Muscle glycogen concentration was higher in the NORM than LOW at all time points in both nutrient and placebo groups (P < 0.05). Postexercise Akt-p70S6K-rpS6 phosphorylation increased in both groups with no differences between legs (P < 0.05). mTOR(Ser2448) phosphorylation in placebo increased 1 h after exercise in NORM (P < 0.05), whereas mTOR increased ~4-fold in LOW (P < 0.01) and ~11 fold in NORM with nutrient (P < 0.01; different between legs P < 0.05). Post-exercise rates of MPS were not different between NORM and LOW in nutrient (0.070 ± 0.022 vs. 0.068 ± 0.018 %/h) or placebo (0.045 ± 0.021 vs. 0.049 ± 0.017 %/h). We conclude that commencing high-intensity REX with low muscle glycogen availability does not compromise the anabolic signal and subsequent rates of MPS, at least during the early (4 h) postexercise recovery period.
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Skeletal muscle is a heterogeneous tissue comprised of fibers with different morphological, functional, and metabolic properties. Different muscles contain varying proportions of fiber types; therefore, accurate identification is important. A number of histochemical methods are used to determine muscle fiber type; however, these techniques have several disadvantages. Immunofluorescence analysis is a sensitive method that allows for simultaneous evaluation of multiple MHC isoforms on a large number of fibers on a single cross-section, and offers a more precise means of identifying fiber types. In this investigation we characterized pure and hybrid fiber type distribution in 10 rat and 10 mouse skeletal muscles, as well as human vastus lateralis (VL) using multicolor immunofluorescence analysis. In addition, we determined fiber type-specific cross-sectional area (CSA), succinate dehydrogenase (SDH) activity, and α-glycerophosphate dehydrogenase (GPD) activity. Using this procedure we were able to easily identify pure and hybrid fiber populations in rat, mouse, and human muscle. Hybrid fibers were identified in all species and made up a significant portion of the total population in some rat and mouse muscles. For example, rat mixed gastrocnemius (MG) contained 12.2% hybrid fibers whereas mouse white tibialis anterior (WTA) contained 12.1% hybrid fibers. Collectively, we outline a simple and time-efficient method for determining MHC expression in skeletal muscle of multiple species. In addition, we provide a useful resource of the pure and hybrid fiber type distribution, fiber CSA, and relative fiber type-specific SDH and GPD activity in a number of rat and mouse muscles.
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We have reported that the acute postexercise increases in muscle protein synthesis rates, with differing nutritional support, are predictive of longer-term training-induced muscle hypertrophy. Here, we aimed to test whether the same was true with acute exercise-mediated changes in muscle protein synthesis. Eighteen men (21 ± 1 yr, 22.6 ± 2.1 kg/m(2); means ± SE) had their legs randomly assigned to two of three training conditions that differed in contraction intensity [% of maximal strength (1 repetition maximum)] or contraction volume (1 or 3 sets of repetitions): 30%-3, 80%-1, and 80%-3. Subjects trained each leg with their assigned regime for a period of 10 wk, 3 times/wk. We made pre- and posttraining measures of strength, muscle volume by magnetic resonance (MR) scans, as well as pre- and posttraining biopsies of the vastus lateralis, and a single postexercise (1 h) biopsy following the first bout of exercise, to measure signaling proteins. Training-induced increases in MR-measured muscle volume were significant (P < 0.01), with no difference between groups: 30%-3 = 6.8 ± 1.8%, 80%-1 = 3.2 ± 0.8%, and 80%-3= 7.2 ± 1.9%, P = 0.18. Isotonic maximal strength gains were not different between 80%-1 and 80%-3, but were greater than 30%-3 (P = 0.04), whereas training-induced isometric strength gains were significant but not different between conditions (P = 0.92). Biopsies taken 1 h following the initial resistance exercise bout showed increased phosphorylation (P < 0.05) of p70S6K only in the 80%-1 and 80%-3 conditions. There was no correlation between phosphorylation of any signaling protein and hypertrophy. In accordance with our previous acute measurements of muscle protein synthetic rates a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure.
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The amplitude of the surface EMG does not reach the level achieved during a maximal voluntary contraction force at the end of a sustained, submaximal contraction, despite near-maximal levels of voluntary effort. The depression of EMG amplitude may be explained by several neural and muscular adjustments during fatiguing contractions, including decreased net neural drive to the muscle, changes in the shape of the motor unit action potentials, and EMG amplitude cancellation. The changes in these parameters for the entire motor unit pool, however, cannot be measured experimentally. The present study used a computational model to simulate the adjustments during sustained isometric contractions and thereby determine the relative importance of these factors in explaining the submaximal levels of EMG amplitude at task failure. The simulation results indicated that the amount of amplitude cancellation in the simulated EMG (∼ 40%) exhibited a negligible change during the fatiguing contractions. Instead, the main determinant of the submaximal EMG amplitude at task failure was a decrease in muscle activation (number of muscle fiber action potentials), due to a reduction in the net synaptic input to motor neurons, with a lesser contribution from changes in the shape of the motor unit action potentials. Despite the association between the submaximal EMG amplitude and reduced muscle activation, the deficit in EMG amplitude at task failure was not consistently associated with the decrease in neural drive (number of motor unit action potentials) to the muscle. This indicates that the EMG amplitude cannot be used as an index of neural drive.
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We aimed to determine if any mechanistic differences exist between a single set (1SET) and multiple sets (i.e. 3 sets; 3SET) of resistance exercise by utilizing a primed constant infusion of [ring-13C6]phenylalanine to determine myofibrillar protein synthesis (MPS) and Western blot analysis to examine anabolic signalling molecule phosphorylation following an acute bout of resistance exercise. Eight resistance-trained men (24+/-5 years, BMI=25+/-4 kg m2) were randomly assigned to perform unilateral leg extension exercise at 70% concentric one repetition maximum (1RM) until volitional fatigue for 1SET or 3SET. Biopsies from the vastus lateralis were taken in the fasted state (Fast) and fed state (Fed; 20 g of whey protein isolate) at rest, 5 h Fed, 24 h Fast and 29 h Fed post-exercise. Fed-state MPS was transiently elevated above rest at 5 h for 1SET (2.3-fold) and returned to resting levels by 29 h post-exercise. However, the exercise induced increase in MPS following 3SET was superior in amplitude and duration as compared to 1SET at both 5 h (3.1-fold above rest) and 29 h post-exercise (2.3-fold above rest). Phosphorylation of 70 kDa S6 protein kinase (p70S6K) demonstrated a coordinated increase with MPS at 5 h and 29 h post-exercise such that the extent of p70S6K phosphorylation was related to the MPS response (r=0.338, P=0.033). Phosphorylation of 90 kDa ribosomal S6 protein kinase (p90RSK) and ribosomal protein S6 (rps6) was similar for 1SET and 3SET at 24 h Fast and 29 h Fed, respectively. However, 3SET induced a greater activation of eukaryotic translation initiation factor 2B (eIF2B) and rpS6 at 5 h Fed. These data suggest that 3SET of resistance exercise is more anabolic than 1SET and may lead to greater increases in myofibrillar protein accretion over time.
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A linear relation between surface electromyogram (EMG) amplitude and muscle force is often assumed and used to estimate the contributions of selected muscles to various tasks. In the presence of muscle fatigue, however, changes in the properties of muscle fibre action potentials and motor unit twitch forces can alter the relation between surface EMG amplitude and force. A novel integrative model of motor neuron control and the generation of muscle fibre action potentials was used to simulate surface EMG signals and muscle force during three fatigue protocols. The change in the simulated relation between surface EMG amplitude and force depended on both the level of fatigue and the details of the fatiguing contraction. In general, surface EMG amplitude overestimated muscle force when fatigue was present. For example, surface EMG amplitudes corresponding to 60 per cent of the amplitude obtained at maximal force without fatigue corresponded to forces in the range 10-40% of the maximal force across three representative fatigue protocols. The results indicate that the surface EMG amplitude cannot be used to predict either the level of muscle activation or the magnitude of muscle force when the muscle exhibits any fatigue.
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Skeletal muscle glycogen metabolism was investigated in eight male subjects during and after six sets of 70% one repetition maximum (1 RM, I-70) and 35% 1 RM (I-35) intensity weight-resistance leg extension exercise. Total force application to the machine lever arm was determined via a strain gauge and computer interfaced system and was equated between trials. Compared with the I-70 trial, the I-35 trial was characterized by almost double the repetitions (13 +/- 1 vs. 6 +/- 0) and half the peak concentric torque for each repetition (12.4 +/- 0.5 vs. 24.2 +/- 1.0 Nm). After the sixth set, muscle glycogen degradation was similar between I-70 and I-35 trials (47.0 +/- 6.6 and 46.6 +/- 6.0 mmol/kg wet wt, respectively), as was muscle lactate accumulation (13.8 +/- 0.7 and 16.7 +/- 4.2 mmol/kg wet wt, respectively). After 2 h of passive recovery without caloric intake, muscle glycogen increased by 22.2 +/- 6.8 and 14.2 +/- 2.5 mmol/kg wet wt in the I-70 and I-35 trials, respectively. Optical absorbance measurement of periodic acid-Schiff-stained muscle sections after the 2 h of recovery revealed larger absorbance increases in fast-twitch than in slow-twitch fibers (0.119 +/- 0.024 and 0.055 +/- 0.024, P = 0.02). Data indicated that when external work was constant, the absolute amount of muscle glycogenolysis was the same regardless of the intensity of resistance exercise. Nevertheless the rate of glycogenolysis during the I-70 trial was approximately double that of the I-35 trial.
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Odorant specificity to l-alpha-amino acids was determined for 245 olfactory bulb (OB) neurons recorded from 121 channel catfish. The initial tests included 4 amino acids representing acidic [monosodium glutamate (Glu)], basic [arginine (Arg)], and neutral [possessing short: alanine (Ala) and long: methionine (Met) side chains] amino acids that were previously indicated to bind to independent olfactory receptor sites. Ninety-one (37%) units (Group I) tested at 1, 10, and 100 microM showed high selectivity and were excited by only one of the 4 amino acids. Odorant specificity for the vast majority of Group I units did not change over the 3 s of response time analyzed. A total of 154 OB units (63%) (Group II) were excited by a second amino acid, but only at >/=10x odorant concentration. An additional 69 Group I units were tested with related amino acids and derivatives from 10(-9) to 10(-5) M to determine their excitatory odorant thresholds and selectivities. Two groups of units originally selective for Met were evident: those most sensitive to neutral amino acids having branched and linear side chains, respectively. OB units originally selective for Ala responded at low concentration to other similar amino acids. Units originally selective for Arg were excited at low concentration by amino acids possessing in their side chains at least 3 methylene groups and a terminal amide or guanidinium group. The specificities of the OB units determined electrophysiologically are sufficient to account for many of the previous results of behavioral discrimination of amino acids in this and related species.
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It is often claimed that strength training of one limb increases the strength of the contralateral limb, but this has not been demonstrated consistently, particularly in well-controlled studies. The aim was to quantitatively combine the results of other studies on the effects of unilateral training on contralateral strength in humans to provide an answer to this physiological question. We analyzed all randomized controlled studies of voluntary unilateral resistance training that used training intensities of at least 50% of maximal voluntary strength for a minimum of 2 wk. Studies were identified by computerized and hand searches of the literature. Data on changes in strength of contralateral and control limbs were extracted and statistically pooled in a meta-analysis. This approach allows conclusions to be based on a statistically meaningful sample size, which might be difficult to achieve in other ways. Seventeen studies met the inclusion criteria, and 13 provided enough data for statistical pooling. The contralateral effects of strength training reported in individual studies varied from -2.7 to 21.6% of initial strength. The pooled estimate of the effect of unilateral resistance training on the maximal voluntary strength of the contralateral limb was 7.8% (95% confidence interval: 4.1-11.6%). This was 35.1% (95% confidence interval: 20.9-49.3%) of the effect on the trained limb. Pooling of all available data shows that unilateral strength training produces modest increases in contralateral strength.
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Simultaneous analyses of glycogen in sections with other subcellular constituents within the same section will provide detailed information on glycogen deposition and the processes involved. To date, staining protocols for quantitative glycogen analyses together with immunofluorescence in the same section are lacking. We aimed to: (1) optimise PAS staining for combination with immunofluorescence, (2) perform quantitative glycogen analyses in tissue sections, (3) evaluate the effect of section thickness on PAS-derived data and (4) examine if semiquantitative glycogen data were convertible to genuine glycogen values. Conventional PAS was successfully modified for combined use with immunofluorescence. Transmitted light microscopic examination of glycogen was successfully followed by semiquantification of glycogen using microdensitometry. Semiquantitative data correlated perfectly with glycogen content measured biochemically in the same sample (r 2=0.993, P<0.001). Using a calibration curve (r 2=0.945, P<0.001) derived from a custom-made external standard with incremental glycogen content, we converted the semiquantitative data to genuine glycogen values. The converted semiquantitative data were comparable with the glycogen values assessed biochemically (P=0.786). In addition we showed that for valid comparison of glycogen content between sections, thickness should remain constant. In conclusion, the novel protocol permits the combined use of PAS with immunofluorescence and shows valid conversion of data obtained by microdensitometry to genuine glycogen data.
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Key points: A classic unresolved issue in human integrative physiology involves the role of exercise intensity, duration and volume in regulating skeletal muscle adaptations to training. We employed counterweighted single-leg cycling as a unique within-subject model to investigate the role of exercise intensity in promoting training-induced increases in skeletal muscle mitochondrial content. Six sessions of high-intensity interval training performed over 2 weeks elicited greater increases in citrate synthase maximal activity and mitochondrial respiration compared to moderate-intensity continuous training matched for total work and session duration. These data suggest that exercise intensity, and/or the pattern of contraction, is an important determinant of exercise-induced skeletal muscle remodelling in humans. Abstract: We employed counterweighted single-leg cycling as a unique model to investigate the role of exercise intensity in human skeletal muscle remodelling. Ten young active men performed unilateral graded-exercise tests to measure single-leg V̇O2, peak and peak power (Wpeak ). Each leg was randomly assigned to complete six sessions of high-intensity interval training (HIIT) [4 × (5 min at 65% Wpeak and 2.5 min at 20% Wpeak )] or moderate-intensity continuous training (MICT) (30 min at 50% Wpeak ), which were performed 10 min apart on each day, in an alternating order. The work performed per session was matched for MICT (143 ± 8.4 kJ) and HIIT (144 ± 8.5 kJ, P > 0.05). Post-training, citrate synthase (CS) maximal activity (10.2 ± 0.8 vs. 8.4 ± 0.9 mmol kg protein-1 min-1 ) and mass-specific [pmol O2 •(s•mg wet weight)-1 ] oxidative phosphorylation capacities (complex I: 23.4 ± 3.2 vs. 17.1 ± 2.8; complexes I and II: 58.2 ± 7.5 vs. 42.2 ± 5.3) were greater in HIIT relative to MICT (interaction effects, P < 0.05); however, mitochondrial function [i.e. pmol O2 •(s•CS maximal activity)-1 ] measured under various conditions was unaffected by training (P > 0.05). In whole muscle, the protein content of COXIV (24%), NDUFA9 (11%) and mitofusin 2 (MFN2) (16%) increased similarly across groups (training effects, P < 0.05). Cytochrome c oxidase subunit IV (COXIV) and NADH:ubiquinone oxidoreductase subunit A9 (NDUFA9) were more abundant in type I than type II fibres (P < 0.05) but training did not increase the content of COXIV, NDUFA9 or MFN2 in either fibre type (P > 0.05). Single-leg V̇O2, peak was also unaffected by training (P > 0.05). In summary, single-leg cycling performed in an interval compared to a continuous manner elicited superior mitochondrial adaptations in human skeletal muscle despite equal total work.
Article
We describe the design, fabrication and testing of a novel multi-channel thin-film electrode for detection of the output of motoneurones in vivo and in humans, through muscle signals. The structure includes a linear array of 16 detection sites that can sample intramuscular electromyographic (EMG) activity from the entire muscle cross-section. The structure was tested in two superficial muscles (the abductor digiti minimi (ADM) and the tibialis anterior (TA)) and a deep muscle (the genioglossus (GG)) during contractions at various forces. Moreover, surface EMG signals were concurrently detected from the TA muscle with a grid of 64 electrodes. Surface and intramuscular signals were decomposed into the constituent motor unit (MU) action potential trains. With the intramuscular electrode, up to 31 MUs were identified from the ADM muscle during an isometric contraction at 15% of the maximal force (MVC) and 50 MUs were identified for a 30% MVC contraction of TA. The new electrode detects different sources than a surface EMG system, as only one MU spike train was found to be common in the decomposition of the intramuscular and surface signals acquired from the TA. The system also allowed access to the GG muscle, which cannot be analysed with surface EMG, with successful identification of MU activity. With respect to classic detection systems, the presented thin-film structure enables recording from large populations of active MUs of deep and superficial muscles and thus can provide a faithful representation of the neural drive sent to a muscle. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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AimHeat shock proteins (HSP) are important chaperones for stressed and damaged proteins. Low-load blood flow restricted resistance exercise (BFRE) is generally believed not to induce significant muscle damage; but is hitherto unverified with intracellular markers. Consequently, the aim of this study was to investigate the HSP response after BFRE in human skeletal muscle.Methods Nine healthy volunteers performed five sets to failure of unilateral knee-extension at 30% of 1RM with partial blood flow restriction. The contralateral leg performed the same work with free blood flow. Muscle biopsies were collected pre, 1, 24 and 48 hours after exercise and analysed for HSP27, αB-crystallin, HSP70, desmin, glycogen content and myosin heavy chain by immunohistochemistry, ELISA and western blotting.ResultsOne hour after exercise cytosolic HSP27 and αB-crystallin levels were reduced and increased in the cytoskeletal fraction in the BFRE-leg. HSP70 showed a delayed response and was increased over 48 hours in the BFRE-leg. Immunohistochemical analyses showed higher staining intensity of HSP70 in type 1 fibres in the BFRE-leg at 24 and 48 h post exercise. PAS staining showed decreased glycogen levels after BFRE, and interestingly, glycogen was still depleted 48 hours after exercise in the same fibres displaying high HSP70 staining (type 1 fibres).Conclusion Translocation of HSP27 and αB-crystallin from cytosol to cytoskeletal structures indicates that cytoskeletal proteins are stressed during BFRE. However, overt signs of myofibrillar disruptions were not observed. Interestingly, the stress response was more pronounced in type 1 than in type 2 fibres and coincided with low glycogen levels.This article is protected by copyright. All rights reserved.
Article
Western blotting has been used for protein analyses in a wide range of tissue samples for >30 years. Fundamental to western blotting success are a number of important considerations, which unfortunately are often overlooked or not appreciated. Firstly, lowly expressed proteins may often be better detected by dramatically reducing the amount of sample loaded. Single cell (fibre) western blotting demonstrates the ability to detect proteins in small sample sizes, 5-10 μg total mass (1-3 μg total protein). That is an order of magnitude less than often used. Using heterogeneous skeletal muscle as the tissue of representation, the need to undertake western blotting in sample sizes equivalent to single fibre segments is demonstrated. Secondly, incorrect results can be obtained if samples are fractionated and a proportion of the protein of interest inadvertently discarded during sample preparation. Thirdly, quantitative analyses demand that a calibration curve be used. This is regardless of using a loading control, which must be proven to not change with the intervention and also be appropriately calibrated. Fourthly, antibody specificity must be proven using whole tissue analyses, and for immunofluorescence analyses it is vital that only a single protein is detected. If appropriately undertaken, western blotting is reliable, quantitative, both in relative and absolute terms, and extremely valuable.
Article
SUMMARY In order to stimulate further adaptation toward specific training goals, progressive resistance training (RT) protocols are necessary. The optimal characteristics of strength-specific programs include the use of concentric (CON), eccentric (ECC), and isometric muscle actions and the performance of bilateral and unilateral single- and multiple-joint exercises. In addition, it is recommended that strength programs sequence exercises to optimize the preservation of exercise intensity (large before small muscle group exercises, multiple-joint exercises before single-joint exercises, and higher-intensity before lower-intensity exercises). For novice (untrained individuals with no RT experience or who have not trained for several years) training, it is recommended that loads correspond to a repetition range of an 8-12 repetition maximum (RM). For intermediate (individuals with approximately 6 months of consistent RT experience) to advanced (individuals with years of RT experience) training, it is recommended that individuals use a wider loading range from 1 to 12 RM in a periodized fashion with eventual emphasis on heavy loading (1-6 RM) using 3- to 5-min rest periods between sets performed at a moderate contraction velocity (1-2 s CON; 1-2 s ECC). When training at a specific RM load, it is recommended that 2-10% increase in load be applied when the individual can perform the current workload for one to two repetitions over the desired number. The recommendation for training frequency is 2-3 dIwkj1 for novice training, 3-4 dIwkj1 for intermediate training, and 4-5 dIwkj1 for advanced training. Similar program designs are recom- mended for hypertrophy training with respect to exercise selection and frequency. For loading, it is recommended that loads corresponding to 1-12 RM be used in periodized fashion with emphasis on the 6-12 RM zone using 1- to 2-min rest periods between sets at a moderate velocity. Higher volume, multiple-set programs are recommended for maximizing hypertrophy. Progression in power training entails two general loading strategies: 1) strength training and 2) use of light loads (0-60% of 1 RM for lower body exercises; 30-60% of 1 RM for upper body exercises) performed at a fast contraction velocity with 3-5 min of rest between sets for multiple sets per exercise (three to five sets). It is also recommended that emphasis be placed on multiple-joint exercises especially those involving the total body. For local muscular endurance training, it is recommended that light to moderate loads (40-60% of 1 RM) be performed for high repetitions (915) using short rest periods (G90 s). In the interpretation of this position stand as with prior ones, recommendations should be applied in context and should be contingent upon an individual's target goals, physical capacity, and training
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Glycogen depletion of muscle fibre types I, IIA, IIAB and IIB was studied using a histochemical method to quantify glycogen content in individual fibres. The reliability was examined in 29 muscle biopsies, in which total glycogen content was compared to average periodic acid Schiff (PAS) stain intensity in sections from the same samples. Over a wide range of glycogen content (1–252 mmole glucosyl units. kg-1 wet weight) a linear relationship (r=0.93) was found between the two methods for quantification of muscle glycogen. Glycogen depletion patterns in type I, IIA, IIAB and IIB fibres were studied in 5 subjects during exhaustive bicycle exercise at 75% of VO2 max. At rest before exercise glycogen content was 16% higher in type II subgroups than in type I (p<0.05).From start of exercise the same glycogen depletion rate was observed in type I and IIA.Glycogen content of Type IIAB and IIB was unchanged during the first part of exercise. Later a decrease was observed, first in type IIAB and finally in IIB, suggesting a decrease in threshold force of these fibre types. The results indicate physiological differences between the 3 subgroups of type II fibres in man, whereas at the present exercise intensity type I and IIA fibres were recruited simultaneously from start.
Article
VØLLESTAD, N.K. & BLOM P.C.S. 1985. Effect of varying exercise intensity on glycogen depletion in human muscle fibres. Acta Physiol Scand125, 395–405. Received 15 December 1984, accepted 30 April 1985. ISSN 0001–6772. Institute of Muscle Physiology, Oslo, Norway.Glycogen depletion of muscle fibre types I, II A, IIAB and IIB was studied during bicycle exercise at 43% (π= 5), 61% (π= 7) and 91% (π= 5) of Vo2 max Glycogen content in individual fibres from vastus lateralis muscles was quantified as optical density of periodic acid-Schiff (PAS) stain. After 60 min at the lowest intensity, glycogen depletion was observed in almost all type I fibres and in about 20% of type IIA fibres. After 60 min exercise at 61 % of Vo2max, glycogen breakdown was observed in all type I fibres and in about 65% of type IIA fibres. During the first part of exercise at 91% of Vo2 max, glycogen breakdown was observed in all type I and IIA and in about 50% of type IIAB and IIB fibres. Muscle lactate concentration increased during the first 5 min of exercise at 91% of Vo2max to 15 mmol kg-1 (w/w) and remained thereafter at this level. From start of exercise the average rates of glycogen depletion in type I fibres were about 1.0,2.0 and 4.3 mmol glucosyl units kg-1 (w/w) min-1 at 43%, 61 % and 91 % of Vo2max The depletion rates were almost constant with time at the two lower intensities. The results indicate that the number of fibres activated from the start increase gradually in response to increased exercise intensity. The rates of glycogen depletion in type I fibres suggest a progressive tension output of these fibres with increasing intensity.
Article
Surface electromyographic (EMG) amplitude from the upper trapezius muscle is widely used as a measure of shoulder-neck load in ergonomic studies. A variety of methods for normalizing EMG amplitude from the upper trapezius (EMGamp(ut)) have been presented in the literature. This impedes meta-analyses of, for instance, upper trapezius load in relation to development of shoulder-neck disorders. The review offers a thorough discussion of different normalization procedures for EMGamp(ut). The following main issues are focused: output variable, location of electrodes, posture and attempted movement during normalization, load and duration of reference contractions, signal processing and test-retest repeatability. It is concluded that translations of EMGamp(ut) into biomechanical variables, for example relative force development in the shoulder or in the upper trapezius itself, suffer from low validity, especially if used in work tasks involving large and/ or fast arm movements. The review proposes a standard terminology relating to normalization of EMGamp(ut) and concludes in a concrete suggestion for a normalization procedure generating bioelectrical variables which reflect upper trapezius activation.
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Periodic acid acts upon the 1,2 glycol linkage (-CHOH -CHOH-) of carbohydrates in tissue sections to produce aldehyde (RCHO+RCHO) which can be colored with Schiff s reagent. The method can be used on frozen or paraffin sections and is useful as a reaction for carbohydrates of tissues: glycogen (in paraffin section only), mucin, basement membrane, reticulin, the colloid of the pituitary stalk and thyroid, some of the acidophile cells of the human anterior hypophysis, the granular cells of the renal arteriole, etc. In abnormal tissues, it colors many of the “hyaline” materials— amyloid infiltrations, arteriolosclerotic hyaline, colloid droplets, mitotic figures, etc. The histochemical uses of the periodic-acid-Schiff's reagent (PAS) need careful control because of the possibility of attachment of iodate or periodate to tissue constitutents, producing a recoloration of the Schiff's reagent. Whenever possible the positive reacting material should be further identified by other methods since Lison showed other substances besides aldehydes can recolorize SchifFs reagent.
Article
This study evaluated the effect of strength training on glycogen utilization in slow twitch (ST) and fast twitch (FT) muscle fibers during repeated maximal unilateral isokinetic leg extensions at 180 degrees.s-1. Strength-trained (5 males, 4 females) and untrained (4 males, 6 females) subjects performed three sets of 50 maximum voluntary contractions (MVC) at this velocity with 10-min rest intervals between sets. Biopsies were taken from the vastus lateralis muscle before and after each exercise session. Glycogen content of the fibers was quantified as optical density (OD) using microspectrophotometric densitometry on serial cross-sections of muscle tissue stained with a periodic acid Schiff reagent stain after individual fibers were identified as ST or FT according to a stain for myofibrillar ATPase activity. Analysis of variance with repeated measures yielded the following results: OD, i.e., glycogen, was reduced similarly in both fiber types after exercise, but only in the males (P = 0.02); there was no significant main effect of training status per se (i.e., strength-trained vs untrained). These results indicate that years of strength training do not change the pattern of muscle fiber-specific glycogen utilization during repeated dynamic MVCs.
Article
The rate of glycogen resynthesis was examined in different muscle fibre types after prolonged exhaustive exercise. Six subjects exercised to exhaustion at 75% of VO2 max, and muscle biopsies were taken after 0, 90 and 180 min of recovery. Glucose drinks (1.4, 0.7 and 0.7 g kg-1 body wt) were taken at time 0, 60 and 120 min. Photometric determination of periodic acid-Schiff stain intensity revealed a 65% faster rate of glycogen resynthesis in type IIA and IIAB as compared to type I fibres during the first 90 min. Thereafter no differences between the various fibre types were detected. No differences in the rate of glycogen resynthesis were observed between the subgroups of type II muscle fibres. These results suggest that there was a slower acceleration of glycogen resynthesis in type I compared to type II fibres. In all fibre types a positive relationship between rate of synthesis and glycogen concentration was observed. It is suggested that the size of the glycogen molecule and hence the number of available terminal glucosyl units is a major determinant of rate of resynthesis.
Article
1. Glycogen depletion pattern in human skeletal muscle fibres was studied after bicycle exercise of varying intensity performed at different pedalling rates. Work intensities studied were equivalent to 30-150% of V(O) (2) max. with pedalling rates of 30-120 rev/min.2. Glycogen depletion increased dramatically with increasing exercise intensity; depletion was 2.7 and 7.4 times greater respectively at workloads demanding 64 and 84% V(O) (2) max. than at workloads calling for 31% V(O) (2) max. Even greater rates of glycogen utilization occurred at supramaximal loads.3. Slow twitch, high oxidative (ST) fibres were the first to lose glycogen (reduced PAS staining) at all workloads below V(O) (2) max. Progressive glycogen depletion occurred in fast twitch (FT) fibres as work continued. Large quantities of glycogen remained in the muscle after 3 hr of exercise at low exercise intensity. This was almost exclusively found in FT fibres. At workloads exceeding maximal aerobic power, there was an initial depletion of glycogen in both fibre types. Varying the pedalling rate and, thus, the total force exerted in each pedal thrust had no effect on the pattern of glycogen depletion in the fibres.4. Results point to primary reliance upon ST fibres during submaximal endurance exercise, FT fibres being recruited after ST fibres are depleted of glycogen. During exertion requiring energy expenditure greater than the maximal aerobic power, both fibre types appeared to be continuously involved in carrying out the exercise.
Article
1. Six healthy males performed sustained contractions with different tensions related to their maximal voluntary contraction (MVC). The isometric exercise consisted of efforts to extend the knee when flexed at an angle of 90 degrees .2. Biopsy samples were taken from the lateral portion of M. quadriceps femoris before and after different periods (6-45 min) during a series of sustained contractions. Total glycogen content was determined on each muscle sample. In order to evaluate whether the glycogen depletion occurred preferentially in slow twitch (ST) or fast twitch (FT) fibres, serial sections of the muscle samples were stained for myofibrillar ATPase and glycogen (PAS reaction).3. In all experiments a selective glycogen depletion was observed. At low tensions, the ST fibres and at higher tensions the FT fibres became glycogen depleted. The critical tension at which this conversion in glycogen depletion from ST to FT fibres took place was 20% MVC.4. It is concluded that at sustained contractions of less than 20% MVC there is a major reliance upon ST fibres and above that level a primary dependence upon FT fibres. It is further suggested that restriction of blood flow and thus availability of oxygen at forces higher than 20% MVC may be the explanation for the present findings.
Article
Glycogen depletion of muscle fibre types I, II A, II AB and II B was studied using a histochemical method to quantify glycogen content in individual fibres. The reliability was examined in 29 muscle biopsies, in which total glycogen content was compared to average periodic acid Schiff (PAS) stain intensity in sections from the same samples. Over a wide range of glycogen content (1-252 mmole glucosyl units . kg-1 wet weight) a linear relationship (r = 0.93) was found between the two methods for quantification of muscle glycogen. Glycogen depletion patterns in type I, II A, II AB and II B fibres were studied in 5 subjects during exhaustive bicycle exercise at 75% of VO2 max. At rest before exercise glycogen content was 16% higher in type II subgroups than in type I (p less than 0.05). From start of exercise the same glycogen depletion rate was observed in type I and II A. Glycogen content of Type II AB and II B was unchanged during the first part of exercise. Later a decrease was observed, first in type II AB and finally in II B, suggesting a decrease in threshold force of these fibre types. The results indicate physiological differences between the 3 subgroups of type II fibres in man, whereas at the present exercise intensity type I and II A fibres were recruited simultaneously from start.
Article
It is common practice for the staining of muscle glycogen with periodic acid-Schiff (PAS) to thaw and dry muscle sections before staining. The goal is to investigate whether this thawing step results in a systematic error that is independent of muscle fiber type and muscle physiological state. Muscle samples from six fasted male subjects were obtained before or after 3 min of high-intensity cycling. Each sample was sectioned; some sections were assessed for muscle fiber composition, and others were either thawed for 20 min or kept frozen before being PAS-stained for glycogen. The response to a 20-min freeze-thaw cycle was also assessed using rested and exercised rats as our experimental model, and the changes in glycogen were measured enzymatically. The inclusion of a 20-min thawing step resulted in a significant reduction (P < 0.05) in the weighted average of the optical density of PAS (ODPAS) staining in both the nonexercised (15 +/- 1.4%) and exercised human muscles (15 +/- 1.3%), with the absolute extent being greater in the nonexercised muscle samples (P < 0.05). Moreover, the observed decrease in ODPAS was greatest in Type IIa fibers for both the nonexercised (P < 0.05) and exercised (P < 0.05) muscle samples. The findings in rats suggest that the muscle damage associated with freeze-thawing is responsible for this stimulation of glycogenolysis. For the quantitative histochemical measurement of glycogen content in skeletal muscle, the common practice of thawing unfixed muscle sections before PAS staining should be abandoned because this causes glycogen breakdown, the extent of which varies across muscle fiber types and prior exercise history.
Article
Previous studies have suggested that regionalization may occur for human motor units, whereby smaller motor units are located in deeper parts of the muscle and larger motor units are located in more superficial portions. We examined this possibility in the human vastus lateralis muscle using macro-EMG (electromyography) to estimate motor unit size. The sample consisted of nine individuals from whom 114 motor units were recorded at forces ranging between 5% and 60% MVC. Peak-to-peak macro-EMG amplitude was well correlated with macro area (Spearman rho = 0.96). There was a statistically significant inverse relationship between recording depth and macro peak-to-peak amplitude (rho = -0.402, p < 0.001). We conclude that there is a nonrandom distribution of motor units in human muscle, with larger motor units located in more superficial regions and smaller units located in deeper regions. Clinicians who monitor motor unit activity need to recognize that a representative sample of motor unit recordings should include motor units from both deeper and more superficial regions of muscle.