ArticleLiterature Review

Neural adaption to resitance training

Authors:
To read the full-text of this research, you can request a copy directly from the author.

Abstract

Strength performance depends not only on the quantity and quality of the involved muscles, but also upon the ability of the nervous system to appropriately activate the muscles. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime movers in specific movements and to better coordinate the activation of all relevant muscles, thereby effecting a greater net force in the intended direction of movement. The evidence indicating neural adaptation is reviewed. Electromyographic studies have provided the most direct evidence. They have shown that increases in peak force and rate of force development are associated with increased activation of prime mover muscles. Possible reflex adaptations related to high stretch loads in jumping and rapid reciprocal movements have also been revealed. Other studies, including those that demonstrate the "cross-training" effect and specificity of training, provide further evidence of neural adaptation. The possible mechanisms of neural adaptation are discussed in relation to motor unit recruitment and firing patterns. The relative roles of neural and muscular adaptation in short- and long-term strength training are evaluated.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the author.

... The rapid increase in strength was maintained throughout the first 6 weeks of training and then the rate of increase largely plateaued. Notably, the temporal nature of this response was remarkably similar to what occurs in humans (see Fig. 11 in Sale 1988 [31]). Thus, as described by Sale 1988, we strongly suspect that the initial increase in strength was largely due to neural adaptations whereas the later increases were mediated by muscular adaptions. ...
... Notably, the temporal nature of this response was remarkably similar to what occurs in humans (see Fig. 11 in Sale 1988 [31]). Thus, as described by Sale 1988, we strongly suspect that the initial increase in strength was largely due to neural adaptations whereas the later increases were mediated by muscular adaptions. ...
... The basis for this argument stems from the data in Figure 2B which reveals that the gains in strength substantially plateaued after the 6 th week of training (i.e., 90% of the total increase in maximal pulling load occurred during the first 6 weeks of training). According to Sale 1998, muscle and strength adaptations plateau at the same time after the onset of PRE [31]. If this point holds true in the weight pulling model, then going from 6-13 . ...
Preprint
Full-text available
This study describes a mouse model of human progressive resistance exercise that utilizes a full-body/multi-joint exercise (weight pulling) along with a training protocol that mimics a traditional human paradigm (3 training sessions per week, ~8-12 repetitions per set, 2 minutes of rest between sets, ~2 maximal-intensity sets per session, last set taken to failure, and a progressive increase in loading that is based on the individual's performance). We demonstrate that weight pulling can induce an increase in the mass of numerous muscles throughout the body. The magnitude of increase in muscle mass is similar to what has been observed in human studies, and it is associated with the same type of long-term adaptations that occur in humans (e.g., fiber hypertrophy, myonuclear accretion, and in some instances a fast-to-slow transition in Type II fiber composition). Moreover, we demonstrate that weight pulling can induce the same type of acute responses that are thought to drive these long-term adaptations (e.g., the activation of signaling through mTORC1 and the induction of protein synthesis at 1 hr post-exercise). Collectively, the results of this study indicate that weight pulling can serve as a highly translatable mouse model of human progressive resistance exercise.
... This involves the integration of information from cognition, the central nervous system, the peripheral nervous system, and the skeletal muscle participating in the movement. 1 To move, i.e. physical function, requires the idea to move, an impulse from cerebral cortex which goes through the central nervous system, down the spinal cord to the motor end plate on skeletal muscle, and then skeletal is then activated to move. 1 As one can see, there is a considerable interaction between skeletal muscle and the nervous system. The idea that anabolic agents can improve function in cachexia (skeletal muscle wasting) without 'training of the nervous system' is somewhat uninformed. ...
... 1 To move, i.e. physical function, requires the idea to move, an impulse from cerebral cortex which goes through the central nervous system, down the spinal cord to the motor end plate on skeletal muscle, and then skeletal is then activated to move. 1 As one can see, there is a considerable interaction between skeletal muscle and the nervous system. The idea that anabolic agents can improve function in cachexia (skeletal muscle wasting) without 'training of the nervous system' is somewhat uninformed. ...
... Resistance exercise training (weight training) increases muscle strength in the first~4-6 weeks without notable increases in muscle mass. 1 Therefore, it is believed that it is almost all adaptations are nervous system adaptations during this first portion of resistance training adaptations. After 4-6 weeks, muscle mass/muscle size improvements are notable and continue for some time if the resistance training is progressive, with regard to added resistance (weight lifted). ...
... first introduced the idea that motor learning was most important for rapid increases in strength, and that increases in muscular size became increasingly important with time. This notion, that neural adaptations underlie strength gain during the first few weeks of resistance training, was then shown by Moritani and deVries (1979) and subsequently discussed in an influential review by Sale (1988). They postulated that, since there were measurable increases in voluntary strength with resistance training, in the absence of changes in muscle size, neuromuscular adaptations in short-term training are dominated by adaptations in the central nervous system. ...
... In the above-mentioned seminal review, Digby Sale (1988) pointed out that resistance training research studies typically involve training programs that are 8-20 weeks, yet serious athletes have training programs that last from months up to years. To this day, it is commonly accepted, and appears in many reviews and textbooks, that most of the strength gain within the first 2-4 weeks of resistance training relies primarily on neural adaptation, whereas further adaptation is limited to muscular adaptation (i.e. ...
... hypertrophy), but we speculate that there are also contributions aris-ing from neural adaptations, indicated by the broken lines. While the relative contribution of muscle hypertrophy to overall strength gain is shown to plateau we would argue that an increase in strength gain will also be, in part, due to contributions arising from muscle hypertrophy (however not shown here) (created with inspiration from Sale 1988). Variability in the frequency, intensity, time, and type of training will cause various neural, and muscular adaptations, and ultimately affect strength, which is indicated by the shaded regions ...
Article
Full-text available
Resistance training enhances muscular force due to a combination of neural plasticity and muscle hypertrophy. It has been well documented that the increase in strength over the first few weeks of resistance training (i.e. acute) has a strong underlying neural component and further enhancement in strength with long-term (i.e. chronic) resistance training is due to muscle hypertrophy. For obvious reasons, collecting long-term data on how chronic-resistance training affects the nervous system not feasible. As a result, the effect of chronic-resistance training on neural plasticity is less understood and has not received systematic exploration. Thus, the aim of this review is to provide rationale for investigating neural plasticity beyond acute-resistance training. We use cross-sectional work to highlight neural plasticity that occurs with chronic-resistance training at sites from the brain to spinal cord. Specifically, intra-cortical circuitry and the spinal motoneuron seem to be key sites for this plasticity. We then urge the need to further investigate the differential effects of acute versus chronic-resistance training on neural plasticity, and the role of this plasticity in increased strength. Such investigations may help in providing a clearer definition of the continuum of acute and chronic-resistance training, how the nervous system is altered during this continuum and the causative role of neural plasticity in changes in strength over the continuum of resistance training.
... The rapid increase in strength was maintained throughout the first 6 weeks of training, and then the rate of increase largely plateaued. Notably, the temporal nature of this response was remarkably similar to what occurs in humans (see Figure 11 in Sale 1988 [31]). Thus, as described by Sale 1988, we strongly suspect that the initial increase in strength was largely due to neural adaptations, whereas the later increases were mediated by muscular adaptions. ...
... Notably, the temporal nature of this response was remarkably similar to what occurs in humans (see Figure 11 in Sale 1988 [31]). Thus, as described by Sale 1988, we strongly suspect that the initial increase in strength was largely due to neural adaptations, whereas the later increases were mediated by muscular adaptions. ...
... The basis for this argument stems from the data in Figure 2B, which reveal that the gains in strength substantially plateaued after the 6th week of training (i.e., 90% of the total increase in maximal pulling load occurred during the first 6 weeks of training). According to Sale 1998, muscle and strength adaptations plateau at the same time after the onset of PRE [31]. If this point holds true in the weight pulling model, then transitioning from 6-13 weeks of training would have only led to a ~10% greater increase in variables such as muscle mass (e.g., a 10% increase in mass after 6 weeks vs. an 11% increase after 13 weeks). ...
Article
Full-text available
This study describes a mouse model of progressive resistance exercise that utilizes a full-body/multi-joint exercise (weight pulling) along with a training protocol that mimics a traditional human paradigm (three training sessions per week, ~8–12 repetitions per set, 2 min of rest between sets, around two maximal-intensity sets per session, last set taken to failure, and a progressive increase in loading that is based on the individual’s performance). We demonstrate that weight pulling can induce an increase in the mass of numerous muscles throughout the body. The relative increase in muscle mass is similar to what has been observed in human studies, and is associated with the same type of long-term adaptations that occur in humans (e.g., fiber hypertrophy, myonuclear accretion, and, in some instances, a fast-to-slow transition in Type II fiber composition). Moreover, we demonstrate that weight pulling can induce the same type of acute responses that are thought to drive these long-term adaptations (e.g., the activation of signaling through mTORC1 and the induction of protein synthesis at 1 h post-exercise). Collectively, the results of this study indicate that weight pulling can serve as a highly translatable mouse model of progressive resistance exercise.
... For example, while exercise promotes significant enhancement of morphological MQ outcomes as reported in previous studies undertaken in frail and older adults with moderate limited functional capacity 17,18 , the same effect has not been observed in physically healthy older adults 19,20 , suggesting that older adults presenting at higher risk for disabilities may have greater capacity to adapt to exercise training with improvements in MQ. Moreover, although muscle strength is augmented to a greater extent and faster than muscle size resulting in increased neuromuscular MQ 16,18,21 , this is also conflicting with previous studies undertaking different assessment methods or assessing different muscles presenting no meaningful change following resistance exercise 19,20 . Thus, it is unclear whether specific study characteristics such as the population included, assessment techniques, or even different intervention characteristics (e.g., exercise mode, alone or combined with nutrition programs) are influencing the magnitude of exercise effects on morphological and neuromuscular MQ features. ...
... In the present study, our findings are that exercise, mainly supervised resistance exercise is effective in improving neuromuscular MQ, although this was only significant in physically healthy older adults. This result is in accordance with previous research demonstrating more neural than morphological adaptations following short-term resistance training programs 16,24,33,37 . Therefore, despite expecting to observe greater effects in those at higher risk for disability (i.e., those presenting with low baseline levels), the paucity of studies examining exercise interventions in older adults with health issues impacting muscle precludes us observing such benefits in those most in need. ...
... Therefore, despite expecting to observe greater effects in those at higher risk for disability (i.e., those presenting with low baseline levels), the paucity of studies examining exercise interventions in older adults with health issues impacting muscle precludes us observing such benefits in those most in need. In addition, most studies involved resistance training programs and strength increase with this exercise modality is expected following the principle of specificity 16 . However, this limited our ability for a more comprehensive analysis concerning different exercise modalities 18,26,27,35 or the combination of exercise with nutrition interventions in older adults. ...
Article
Full-text available
To systematically review and analyse the effects of exercise on morphological and neuromuscular muscle quality (MQ) outcomes in older adults and assess a range of possible moderators that may affect the impact of exercise on MQ outcomes. Using PRISMA guidelines, randomised controlled trials were searched in CINAHL, EMBASE, LILACS, PubMed, SciELO, Web of Science, MedNar, OpenGrey and OpenThesis databases. Eligible trials examined the effects of exercise interventions on morphological and neuromuscular MQ in older adults (≥ 60 years). Twenty‑one trials (n = 973 participants) were included. Exercise significantly improved morphological MQ (effect size (ES) = 0.32, 95% CI 0.13–0.51, P < 0.001) with significant results maintained for studies assessing muscle density and intermuscular adipose tissue (ES = 0.45–0.52, P < 0.05). For neuromuscular MQ, exercise provided significant positive effects (ES = 0.49, 95% CI 0.29–0.69, P < 0.001) but only maintained for physically healthy participants (ES = 0.43, P < 0.001), resistance exercise interventions (ES = 0.64, P < 0.001), or studies assessing 1‑RM or knee extensor isokinetic muscle strength relative to leg lean mass (ES = 0.48–0.62, P = 0.001). Associations between exercise duration and changes in MQ measures were not observed (P > 0.05). Supervised exercise interventions significantly improved different measures of MQ regardless of exercise duration, although these effects were small‑to‑moderate and not supported across all population‑, exercise‑, and methods‑related features.
... Increases in muscular strength following a resistance training program can be attributed to neural and hypertrophic factors [23,42,46,57,58,60,64]. Thus, voluntary strength increases due to not only the quantity and quality of muscle mass, but also to the extent that the muscle mass is able to activate [6,58]. ...
... Increases in muscular strength following a resistance training program can be attributed to neural and hypertrophic factors [23,42,46,57,58,60,64]. Thus, voluntary strength increases due to not only the quantity and quality of muscle mass, but also to the extent that the muscle mass is able to activate [6,58]. In general, neural factors are believed to account for most of the increases in strength in the early stage of a resistance training program, whereas hypertrophic factors gradually become prevalent after several weeks of training [23,36,38,40,46,47,58]. ...
... Thus, voluntary strength increases due to not only the quantity and quality of muscle mass, but also to the extent that the muscle mass is able to activate [6,58]. In general, neural factors are believed to account for most of the increases in strength in the early stage of a resistance training program, whereas hypertrophic factors gradually become prevalent after several weeks of training [23,36,38,40,46,47,58]. Hence, initial improvements in strength and muscular performance reported following short-term resistance training are generally attributed to neural adaptation instead of muscle fiber hypertrophy [1,46]. ...
Article
Full-text available
Purpose: To examine and compare the effects of three days of dynamic constant external resistance (DCER) and isokinetic (ISOK) training and subsequent detraining on thigh muscle cross-sectional area (TMCSA) and thigh lean mass (TLM), ISOK peak torque (PT), DCER strength, isometric force, muscle activation, and percent voluntary activation (%VA). Methods: Thirty-one apparently-healthy untrained men (mean ± SD age = 22.2 ± 4.2 years; body mass = 77.9 ± 12.9 kg; height = 173.9 ± 5.4 cm) were randomly assigned to a DCER training group (n = 11), ISOK training group (n = 10) or control (CONT) group (n = 10). Subjects visited the laboratory eight times. The first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for unilateral training of the quadriceps (if assigned to a training group), and the last three visits were the post-training assessments conducted at three days, one week, and two weeks after training ended. Results: DCER strength increased from pre- to post-training assessment 1 in both limbs for the DCER group only, and remained elevated during post-training assessments 2 and 3 (P < 0.05). In addition, surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment, and post-training assessments 1 and 2 (P < 0.05). No other training-related changes were found. Conclusion: The primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training. This has important implications for injury rehabilitation, where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.
... Voluntary force modulation in humans is the ability to tune the force applied during motion. Given the complexity of the neural system and its non-trivial interactions with the musculoskeletal system, the mechanisms behind voluntary force modulation are still not well understood [1][2][3]. To address these mechanisms, it is necessary to evaluate the factors contributing to muscle force and identify those that enable real-time force modulations. ...
... In past research, the association of the two parameters with different motor adaptations has been widely examined. For example, Sale et al. [3] extensively reviewed evidence of the neural origins of muscle force, showing that increases in peak force and force rate development are associated with the increased activation of prime mover muscles. In this regard, the study of the distribution of muscle activity across large muscles during different force conditions could elucidate the relationship between their coordination and the modulation of force. ...
Article
Full-text available
Voluntary force modulation is defined as the ability to tune the application of force during motion. However, the mechanisms behind this modulation are not yet fully understood. In this study, we examine muscle activity under various resistance levels at a fixed cycling speed. The main goal of this research is to identify significant changes in muscle activation related to the real-time tuning of muscle force. This work revealed significant motor adaptations of the main muscles utilized in cycling as well as positive associations between the force level and the temporal and spatial inter-cycle stability in the distribution of sEMG activity. From these results, relevant biomarkers of motor adaptation could be extracted for application in clinical rehabilitation to increase the efficacy of physical therapy.
... Electromyographic nerve testing in multiple muscle groups has shown significantly more motor unit activation in muscle with specific training compared with untrained muscle. 39 In 1 such study, 6 weeks of training of the first dorsal interosseous muscle led to significant synchronization of motor units. 28 Lack of synchronization leads to lesser power output due to uncoordinated muscle contraction. ...
... 28 Lack of synchronization leads to lesser power output due to uncoordinated muscle contraction. 39 Limited data exist to show the optimal timing for maximizing neural coordination; however, a lack of sufficient neural adaptation preseason may have led to inefficient recruitment of motor units and increased injury risk due to already unconditioned musculature. While we cannot confirm from the available data that the increased injury incidence during the 2020 MLB season is solely attributable to deconditioning, the correlation between a spike in injury incidence and an extended off-season with delayed preseason training suggests that deconditioning of both the musculoskeletal and nervous systems may have played a role. ...
Article
Full-text available
Background The 2020 Major League Baseball (MLB) season was drastically altered because of the COVID-19 pandemic. The changes included an extended layoff between March and July as well as a shortened preseason. Purpose/Hypothesis To determine the incidence and epidemiology of MLB injuries in the abbreviated 2020 season compared with prior seasons. We hypothesized that there was an increase in the overall injury rate in the 2020 season compared with the 2018-2019 seasons and that it equally affected all body regions. Study Design Descriptive epidemiology study. Methods The MLB transactions database was queried to find players who had been placed on the injury list between 2018 and 2020. Injuries were categorized into upper extremity, lower extremity, spine/core, and other injuries. Incidence per 1000 athlete-exposures was calculated for the prior 2 seasons (2018-2019) and for the 2020 season separately. Incidence for each category was also calculated separately for pitchers and fielders. Incidence rate ratios (IRRs) and confidence intervals were used to compare injury rates in 2018-2019 versus 2020. The z test for proportions was used to determine significant differences between injury incidences. Results In 2020, the overall incidence rate per 1000 athlete-exposures was almost twice the rate compared with the 2 seasons before COVID-19 (8.66 vs 5.13; IRR, 1.69 [95% CI, 1.53-1.87]; P < .001). Injury incidence increased similarly in 2020 for both pitchers (IRR, 1.68 [95% CI, 1.47-1.91]; P < .001) and fielders (IRR, 1.68 [95% CI, 1.45-1.96]; P < .001). Increases in injury incidence were seen in the upper extremity, spine/core, and other injury categories; however, the incidence of the lower extremity did not change significantly. Conclusion There was a significant increase in injury incidence for both pitchers and fielders in 2020. Injury rates increased in anatomic zones of the upper extremity and spine/core but were not significantly changed in the lower extremity. The overall increase in injury rate suggests that irregular or insufficient sport-specific preparation prior to the start of the season placed athletes at a greater risk of injury when play resumed.
... There is also a lack of information on how habituation to CAF may impact the ergogenic effect of CAF in women because most previous studies did not select female participants habituated to CAF [4,[32][33][34]. Habitual CAF intake modifies physiological responses to acute ingestion of this stimulant by the up-regulation of adenosine receptors [33,35]. In animal models, the acute ingestion of CAF (10 mg/kg/b.m./day for two weeks) increased the number of binding sites for adenosine in the brain cortex [36]. ...
... Conflicting results between the presented studies and those of Wilk et al. [7] can be related to the gender difference of the subjects (male vs. female). Sex may have a significant effect on skeletal muscle morphology and function [35], muscle substrate utilization and neuromuscular activation [56]. Women commonly have a higher proportion of type I fibers, greater muscle capillary density [57] with distinct glycolytic and oxidative capacities [58,59]. ...
Article
Full-text available
Purpose The main goal of this study was to assess the acute effects of 3 and 6 mg of caffeine intake per kg of body mass (b.m.) on maximal strength and strength-endurance in women habituated to caffeine. Methods Twenty-one healthy resistance-trained female students (23.0 ± 0.9 years, body mass: 59.0 ± 6.6 kg), with a daily caffeine intake of 5.8 ± 2.6 mg/kg/b.m. participated in a randomized, crossover, double-blind design. Each participant performed three experimental sessions after ingesting either a placebo (PLAC) or 3 mg/kg/b.m. (CAF-3) and 6 mg/kg/b.m. (CAF-6) of caffeine. In each experimental session, the participants underwent a 1RM test and a strength-endurance test at 50 %1RM in the bench press exercise. Maximal load was measured in the 1RM test and the time under tension, number of preformed repetitions, power output and bar velocity were registered in the strength-endurance test. Results The one-way ANOVA showed a main effect of caffeine on 1RM bench press performance (F = 14.74; p < 0.01). In comparison to the PLAC (40.48 ± 9.21 kg), CAF-3 (41.68 ± 8.98 kg; p = 0.01) and CAF-6 (42.98 ± 8.79 kg; p < 0.01) increased 1RM bench press test results. There was also a significant increase in 1RM for CAF-6 when compared to CAF-3 ( p < 0.01). There was a main effect of caffeine on time under tension during the strength-endurance test (F = 13.09; p < 0.01). In comparison to the PLAC (53.52 ± 11.44 s), CAF-6 (61.76 ± 15.39 s; p < 0.01) significantly increased the time under tension during the maximal strength-endurance test. Conclusion An acute dose of 3-to-6 mg/kg/b.m. of caffeine improves maximum strength. However, these doses of caffeine had minimal ergogenic effect on strength-endurance performance in women habituated to caffeine.
... In face of the results available in the current literature, MIP improvements had a plateau between 6 and 9 weeks in young individuals (Romer and McConnell, 2003), 5 weeks for hypertensive adults (Ferreira et al., 2013), and 2 weeks for older women (Rodrigues et al., 2018(Rodrigues et al., , 2020, as also demonstrated in the current data. In general, the initial gain of any strength training program has been attributed primarily to neural adaptations that occur in the first weeks (Sale, 1988). Behind the early adaptations in MIP provoked by IMT, there are several plausible neural mechanisms that involve the high number of motor units recruited, an increased motor unit firing rate, an improvement in synchrony of motor unit firing, a lower co-activation of antagonist muscle groups, or a combination of these mechanisms (Sale, 1988;Romer and McConnell, 2003). ...
... In general, the initial gain of any strength training program has been attributed primarily to neural adaptations that occur in the first weeks (Sale, 1988). Behind the early adaptations in MIP provoked by IMT, there are several plausible neural mechanisms that involve the high number of motor units recruited, an increased motor unit firing rate, an improvement in synchrony of motor unit firing, a lower co-activation of antagonist muscle groups, or a combination of these mechanisms (Sale, 1988;Romer and McConnell, 2003). Otherwise, it was reported that IMT could also induce morphological adaptations as described by the increased diaphragm thickness after eight weeks of IMT in older adults (Souza et al., 2014). ...
Article
Inspiratory muscle training improved maximal inspiratory pressure (MIP) and vagal-mediated heart rate variability (HRV) in older women. However, it is unknown what occurs if the training is discontinued (detraining protocol). The aim of this study was to investigate the IMT and detraining effects on resting HRV in older women. Twelve healthy older women (60–72 yrs) enrolled in home-based IMT at 50% MIP (IMT-group) or placebo at 5% MIP (Sham-group) protocol for 4 weeks using a mechanical pressure threshold loading device. The participants were not engaged in any other exercise protocol at that time. During IMT and Sham interventions, the inspiratory load was adjusted weekly by the actual MIP and resting heart rate variability (HRV) evaluated. After training cessation (4 weeks of detraining), participants returned to the lab for HRV and MIP recordings. Adherence to IMT was superior to 95%. IMT increased MIP (23 ± 8 cmH2O) and vagal-mediated HRV (normalized HF; 37 ± 8%), following by the reduction of sympatho-vagal balance (LF/HF), from the second week to the end of the protocol compared to sham-group. After detraining, IMT-group reduced MIP (−23 ± 8 cmH2O) and vagal-mediated HRV (normalized HF; −38 ± 14%) returning to baseline values. In conclusion, MIP and vagal-HRV improvements induced by IMT were reversed by four weeks of detraining.
... Stiffer tendons and connective tissue matrixes alter force transmission through the muscle-tendon unit, and may therefore present disconnects between muscle and joint level data (44)(45)(46)(47). Furthermore, even though strength gains attributed to neural adaptations occur primarily within the first few weeks of training, whereas muscle architectural adaptations are thought to contribute more long term (48,49), the neural component of mechanical function warrants consideration when interpreting mechanical adaptations obtained from in vivo voluntary contractions (50). Altogether, there is a lack of human data where enough confounding variables are eliminated to make a direct assessment of how muscle architecture influences mechanical function possible. ...
... As such, currently there is little direct evidence in humans supporting the hypothesis that longitudinal fascicle growth can increase V max . Furthermore, neural adaptations and adaptations in tendon stiffness are common following resistance training, including isometric training (41,56,94), and likely contribute to shortening velocity at the joint level (49,50,101,102). Techniques such as correlation coefficients or linear regression (97,98), or normalizing velocity to FL (63, 100) may help better clarify the individual contributions from neural, tendon, and FL adaptations to in vivo shortening velocity in humans. ...
Article
Skeletal muscle has the remarkable ability to remodel and adapt, such as the increase in serial sarcomere number (SSN) or fascicle length (FL) observed after overstretching a muscle. This type of remodelling is termed longitudinal muscle fascicle growth, and its impact on biomechanical function has been of interest since the 1960s due to its clinical applications in muscle strain injury, muscle spasticity, and sarcopenia. Despite simplified hypotheses on how longitudinal muscle fascicle growth might influence mechanical function, existing literature presents conflicting results partly due to a breadth of methodologies. The purpose of this review is to outline what is currently known about the influence of longitudinal muscle fascicle growth on mechanical function and suggest future directions to address current knowledge gaps and methodological limitations. Various interventions indicate longitudinal muscle fascicle growth can increase the optimal muscle length for active force, but whether the whole force-length relationship widens has been less investigated. Future research should also explore the ability for longitudinal fascicle growth to broaden the torque-angle relationship's plateau region, and the relation to increased force during shortening. Without a concurrent increase in intramuscular collagen, longitudinal muscle fascicle growth also reduces passive tension at long muscle lengths; further research is required to understand whether this translates to increased joint range of motion. Lastly, some evidence suggests longitudinal fascicle growth can increase maximum shortening velocity and peak isotonic power, however, there has yet to be direct assessment of these measures in a neurologically intact model of longitudinal muscle fascicle growth.
... Changes in the nervous system contribute to the development of muscle strength after a period of RT (Sale 1988). Indeed, physical strength can be improved in the absence of hypertrophy (Enoka 1997), by enhancing the brain's ability to recruit muscles to contract and produce a desired movement. ...
... These neurological adaptations to RT are difficult to reveal and there are multiple neurological elements that contribute to both the quantity and quality of muscle fibre activation. Some key points related to the neural adaptations to RT are the following statements: (i) increased activation of agonist muscles, (ii) reduction in the co-activation of antagonists and (iii) better co-activation of synergists (Sale 1988). ...
Chapter
Strength training, also known as weight or resistance training (RT), has become one of the most popular forms of exercise, not only for sport performance but also for improving health-related fitness. A wide variety of physiological adaptations achieved through RT have been documented in the short, medium, and long term. These improvements include changes in body composition, muscle hypertrophy, strength, power and motor performance; as well as other health benefits such as changes in blood pressure, insulin sensitivity, lipid profile, endocrine system, and better performance in daily life activities, among others. This chapter will cover the basic physiological adaptations of RT discussing neurological, musculoskeletal, cardiorespiratory, and endocrine responses and adaptations according to current scientific literature. These physiological concepts will be applied in following chapters in which specific methods and technologies for RT are presented.
... Regular practice of strength training is associated to increases in maximal strength, changes in neuromuscular function, and in muscle morphology. Neural adaptations to strength training occur earlier than muscle adaptations and the initial gains in strength are not accompanied by an increase in muscle size [1][2][3]. Furthermore, changes in the neural drive have been inferred from surface electromyography (EMG) studies that show increases in EMG activity of the agonist muscle during first weeks of training [1][2][3][4][5]. ...
... Neural adaptations to strength training occur earlier than muscle adaptations and the initial gains in strength are not accompanied by an increase in muscle size [1][2][3]. Furthermore, changes in the neural drive have been inferred from surface electromyography (EMG) studies that show increases in EMG activity of the agonist muscle during first weeks of training [1][2][3][4][5]. This increase in EMG reflects increases in fiber recruitment or firing frequency [1,4]. ...
Article
Full-text available
Muscle coordination in human movement has been assessed through muscle synergy analysis. In sports science, this procedure has been mainly applied to the comparison between highly trained and unexperienced participants. However, the lack of knowledge regarding strength training exercises led us to study the differences in neural strategies to perform the power clean between weightlifters and untrained individuals. Synergies were extracted from electromyograms of 16 muscles of ten unexperienced participants and seven weightlifters. To evaluate differences, we determined the pairwise correlations for the synergy components and electromyographic profiles. While the shape of activation patterns presented strong correlations across participants of each group, the weightings of each muscle were more variable. The three extracted synergies were shifted in time with the unexperienced group anticipating synergy #1 (−2.46 ± 18.7%; p < 0.001) and #2 (−4.60 ± 5.71%; p < 0.001) and delaying synergy #3 (1.86 ± 17.39%; p = 0.01). Moreover, muscle vectors presented more inter-group variability, changing the composition of synergy #1 and #3. These results may indicate an adaptation in intermuscular coordination with training, and athletes in an initial phase of training should attempt to delay the hip extension (synergy #1), as well as the upper-limb flexion (synergy #2).
... This is evidenced by studies showing: (a) much larger effect sizes for increases in strength compared to hypertrophy, 27 (b) studies showing contralateral strength adaptations, 28 (c) a potentially lesser stimulus for equivalent strength increases compared to hypertrophy (e.g., single sets seem to produce similar strength increases to multiple set training, whereas multiple sets seem to produce greater hypertrophic adaptations compared to single sets 29 ), and (d) that strength increases precede muscle size increases due to neural adaptations and development of the motor schema. 30 In this sense, it might be that increasing strength requires a lesser stimulus and thus training at a lesser intensity of effort (e.g., not to failure) might produce equivocal adaptations compared to training to failure, whereas hypertrophy requires a greater stimulus and thus requires a greater intensity of effort. ...
... Secondly, Grgic et al. 11 In practice, this makes logical sense if we reasonably assume that someone naïve to resistance training will likely make adaptations in response to even a modest stimulus since their threshold for adaptation is low. 30 In addition, another recent meta-analysis of 119 studies 27 reported ESs of 1.43 for strength and 0.54 (reported standardized mean differences corrected by the bias; Hedges' g)for muscle mass for resistance training interventions when compared to non-training control conditions in previously untrained people, which is to say, resistance training compared to doing nothing. 27 However, our re-analysis of 111 of the studies from which we could extract data using multilevel modelling with robust variance estimation has produced effect sizes of 0.88 (95%CI: 0.80 to 0.98) and 0.37 (95%CI: 0.32 to 0.43) for strength and hypertrophy, respectively. ...
... The quick transition from the eccentric to the concentric phase of the movement is known as the stretch-shortening cycle (SSC) [7]. In the eccentric pre-activation phase of plyometrics, the Golgi tendon organs are stretched more than in regular strength training which leads to a greater inhibition of their protective function and leads to an increase in concentric power output [1,8]. Thus, PT can improve the mechanical characteristics of the muscle-tendon complex, strengthen the elastic properties of connective tissue and optimise cross-bridge mechanics and motor unit activation [7,9]. ...
... Thus, PT can improve the mechanical characteristics of the muscle-tendon complex, strengthen the elastic properties of connective tissue and optimise cross-bridge mechanics and motor unit activation [7,9]. These adaptations are associated with improvements in muscle strength, dynamic stability and neuromuscular control, as well as with an increase in contraction speed and joint stiffness [7,8]. In addition, the recent literature has demonstrated the efficacy of PT in different healthrelated contexts [10]. ...
Article
Full-text available
Background Plyometric training (PT) has been widely studied in sport science. However, there is no review that determines the impact of PT on the structural variables and mechanical properties of the lower limbs and physical performance. Objective The aim of this systematic review and meta-analysis was to determine the effects of PT on lower body muscle architecture, tendon structure, stiffness and physical performance. Methods Five electronic databases were analysed. The inclusion criteria were: (1) Availability in English; (2) Experimental studies that included a PT of at least eight sessions; and (3) Healthy adults subjects. Four meta-analyses were performed using Review Manager software: (1) muscle architecture; (2) tendon structure; (3) muscle and tendon stiffness; (4) physical performance. Results From 1008 search records, 32 studies were eligible for meta-analysis. Muscle architecture meta-analysis found a moderate effect of PT on muscle thickness (Standard Mean Difference (SMD): 0.59; [95% Confidence Interval (CI) 0.47, 0.71]) and fascicle length (SMD: 0.51; [95% CI 0.26, 0.76]), and a small effect of PT on pennation angle (SMD: 0.29; [95% CI 0.02, 0.57]). The meta-analysis found a moderate effect of PT on tendon stiffness (SMD: 0.55; [95% CI 0.28, 0.82]). The lower body physical performance meta-analysis found a moderate effect of PT on jumping (SMD: 0.61; [95% CI 0.47, 0.74]) and strength (SMD: 0.57; [95% CI 0.42, 0.73]). Conclusion PT increased the thickness, pennation angle and fascicle length of the evaluated muscles. In addition, plyometrics is an effective tool for increasing tendon stiffness and improving jump and strength performance of the lower body.
... Improvements in this neuromuscular mechanism occur when muscle contractions against high loads are sustained by a lower neural recruitment [51][52][53]. Muscular strength may significantly increase during the first 2-3 months in untrained individuals because of a process that is mainly associated with neural adaptations and muscle activation by neural excitation [54]. However, gains in strength in the long term are generally attributed to an increase in the cross-sectional area of the muscle fiber [55,56] and the accumulation of metabolites [57]. ...
Article
Full-text available
Inadequate protein intake and low levels of physical activity are common long-term sequelae after bariatric surgery and can negatively affect muscle strength (MS) and physical function (PF). The study investigated the effects of resistance training with or without protein supplementation on MS and PF. The study, which involved a 12-week controlled trial (n = 61) of individuals 2–7 years post-Roux-en-Y gastric bypass (RYGB), comprised four groups: whey protein supplementation (PRO; n = 18), maltodextrin placebo (control [CON]; n = 17), resistance training combined with placebo (RTP; n = 11), and resistance training combined with whey protein supplementation (RTP+PRO; n = 15). An isokinetic dynamometer was used to measure MS (peak torque at 60°/s and 180°/s). PF was measured with the 30-s sit-to-stand (30-STS), 6-min walk (6-MWT), and timed up-and-go (TUG) tests. There were improvements in the absolute and relative-to-bodyweight peak torque at 60°/s and 180°/s, TUG, 6-MWT and 30-STS in the RTP and RTP+PRO groups, but not in the CON and PRO groups. Changes in MS were significantly correlated with changes in PF between the pre- and post-intervention periods. A supervised resistance training program, regardless of protein supplementation, improved MS and PF in the mid-to-long-term period after RYGB and can lead to clinical benefits and improved quality of life.
... Pooled MD showed that RT improved various gait parameters after burns. This effects can be attributed to the neuroplasticity of RT, including increased activation of synergistic muscles, increased prime mover motor unit activation and decreased activation of antagonistic muscles [37]. Gait parameters are used to determine limb function and guide on rehabilitation evaluation and treatment. ...
Article
Full-text available
Aim The aim of this study was to evaluate effectiveness and safety of resistance training (RT). Data were retrieved from Medline, EMBASE, PubMed, CINAHL and Cochrane Central Register of Controlled Trials (Central) databases from inception to April 2020. Quantitative studies on RT for muscle strength, lean body mass, cardiopulmonary function, metabolism, quality of life, and pain in burned children were included in this study. Twelve RCTs (379 patients) were identified. Meta-analysis showed RT significant increase in muscle strength [SMD = 2.18, 95% CI (0.79, 3.56), p = 0.002]. However, training showed no significant effect on muscle endurance [MD = 10.00, 95% CI (− 0.22, 20.22), p = 0.06]. Notably, training significantly increases total lean body mass [MD = 2.10, 95% CI (1.28, 2.92), p < 0.001]. In addition, training significantly increased leg lean body mass [MD = 2.10, 95% CI (1.28, 2.92), p < 0.001]. Moreover, training significantly increased VO2peak [MD = 5.83, 95% CI (3.52, 8.13), p < 0.001]. Meta-analysis showed that training significantly increases gait parameters, including stride length, step length, velocity and cadence. Furthermore, training significantly increased explosive capacity of lower limb muscles (p < 0.001). Meta-analysis of 6-min walking test results showed that training significantly improves walking speed (p = 0.0008). Notably, all studies showed unclear or high risk of bias; whereas, quality of the evidence was moderate or low. Analysis showed that RT significantly improves clinical outcomes. However, more high-quality, double-blind, randomized control trials should be performed to explore the effects of RT to ensure successful implementation in rehabilitation.
... In the current study mobility level improved from days 1 to 10 (although it remained below normal levels) despite a reduction in rectus femoris cross-sectional area, the thickness of the anterior compartment of the quadriceps muscle, and handgrip strength over this period. Mobility level in the ICU depends not only on the function, mass, or quality of the muscles but also on the neural adaptation and cardiorespiratory functional reserve, which was especially impaired in the first days of the ICU admission (Sale, 1988;Hodgson C. L. et al., 2014;McGregor et al., 2014). The improvement in the mobility level was accompanied by the reestablishment of the respiratory function over time. ...
Article
Full-text available
Background: Intensive care patients commonly develop muscle wasting and functional impairment. However, the role of severe COVID-19 in the magnitude of muscle wasting and functionality in the acute critical disease is unknown. Objective: To perform a prospective characterization to evaluate the skeletal muscle mass and functional performance in intensive care patients with severe COVID-19. Methods: Thirty-two critically ill patients (93.8% male; age: 64.1 ± 12.6 years) with the diagnosis of the severe COVID-19 were prospectively recruited within 24 to 72 h following intensive care unit (ICU) admission, from April 2020 to October 2020, at Hospital Sírio-Libanês in Brazil. Patients were recruited if older than 18 years old, diagnosis of severe COVID-19 confirmed by RT-PCR, ICU stay and absence of limb amputation. Muscle wasting was determined through an ultrasound measurement of the rectus femoris cross-sectional area, the thickness of the anterior compartment of the quadriceps muscle (rectus femoris and vastus intermedius), and echogenicity. The peripheral muscle strength was assessed with a handgrip test. The functionality parameter was determined through the ICU mobility scale (IMS) and the International Classification of Functioning, Disability and Health (ICF). All evaluations were performed on days 1 and 10. Results: There were significant reductions in the rectus femoris cross-section area (−30.1% [95% IC, −26.0% to −34.1%]; P < 0.05), thickness of the anterior compartment of the quadriceps muscle (−18.6% [95% IC, −14.6% to 22.5%]; P < 0.05) and handgrip strength (−22.3% [95% IC, 4.7% to 39.9%]; P < 0.05) from days 1 to 10. Patients showed increased mobility (0 [0–5] vs 4.5 [0–8]; P < 0.05), improvement in respiratory function (3 [3–3] vs 2 [1–3]; P < 0.05) and structure respiratory system (3 [3–3] vs 2 [1–3]; P < 0.05), but none of the patients returned to normal levels. Conclusion: In intensive care patients with severe COVID-19, muscle wasting and decreased muscle strength occurred early and rapidly during 10 days of ICU stay with improved mobility and respiratory functions, although they remained below normal levels. These findings may provide insights into skeletal muscle wasting and function in patients with severe COVID-19.
... Moritani and Devries (1979) suggested that strength is driven by both neural and hypertrophic adaptations, with hypertrophy becoming more important for strength as time progresses. This model of strength adaptation was discussed in a review by Digby Sale (1988), which has been cited over 1600 times as of August 2020. Although this model is well accepted in the literature, there is a lack of experimental data demonstrating that increasing muscle size has an appreciable impact on muscle strength (Buckner et al., 2016). ...
Article
Previous work in non‐resistance trained individuals has found that an increase in muscle size has no additive effect on changes in strength. However, is thought that muscle growth is of increased importance for resistance trained individuals. Purpose Experiment 1: To examine changes in muscle thickness (MT), and one repetition maximum (1RM) strength following 8 weeks of bi‐weekly 1RM practice or traditional training. Experiment 2: To determine if increasing muscle size increases strength potential when followed by 4 weeks of 1RM training. Methods Participants performed biceps curls for 8 weeks (Experiment 1). One arm performed 4 sets of as many repetitions as possible with approximately 70% of 1RM (TRAD), and the other arm performed a single 1RM. For experiment 2, both arms trained for muscle size and strength. Results Experiment 1 (n=25): For MT, the posterior probabilities favored the hypothesis that MT changed more in the TRAD condition [mean difference: 50% site 0.15 (‐0.09, 0.21) cm; 60% site 0.14 (0.06, 0.23) cm; 70% site 0.17 (0.10, 0.23) cm]. For 1RM strength, each condition changed equivalently. Experiment 2 (n=18): For MT, the posterior probabilities favored the hypothesis that MT changed similarly between conditions following a 4 week strength phase. For changes in 1RM strength, the evidence favored neither hypothesis (i.e. null vs. alternative). Of note, the mean difference between conditions was small [0.72 (4.3) kg]. Conclusions 1RM training produces similar increases in strength as traditional training. Experiment 2 suggests that increases in muscle mass may not increase the “potential” for strength gain.
... An underlying neural mechanism for improvements of mechanical variables can be assessed by surface electromyography (EMG) [21,22]. They can be divided into single-joint or, more complex, multi-joint, or whole-body neural adaptations [22]. ...
Article
Full-text available
Background: Muscle coordination is important for rational and effective planning of therapeutic and exercise interventions using equipment that mimics functional movements. Our study was the first to assess muscle coordination during flywheel (FW) squats. Methods: Time-of-peak electromyographic activation order was assessed separately for 8, 4, and 3 leg muscles under four FW loads. A sequential rank agreement permutations tests (SRA) were conducted to assess activation order and Kendall's tau was used to assess the concordance of activation order across subjects, loads and expected order of activation. Results: SRA revealed a latent muscle activation order at loads 0.05, 0.075, and 0.1, but not at 0.025 kg·m2. Kendall's tau showed moderate-to-strong concordance between the expected (proximal-to-distal) and the observed muscle activation order only at a load 0.025 kg·m2, regardless of the number of muscles analyzed. Muscle activation order was highly concordant between loads 0.05, 0.075, and 0.1 kg·m2. Conclusions: The results show a specific role of each muscle during the FW squat that is load-dependent. While the lowest load follows the proximal-to-distal principle of muscle activation, higher loads lead to a reorganization of the underlying muscle coordination mechanisms. They require a specific and stable muscle coordination pattern that is not proximal-to-distal.
... Strength is considered a skilled act where agonists must be maximally activated, whilst supported by appropriate synergist and stabiliser activation and opposed by minimal antagonist co-activation [118]. Poor intermuscular coordination would limit the ability to express the available muscle strength functionally [103,108,111]. ...
Article
Full-text available
It is important to optimise the functional recovery process to enhance patient outcomes after major injury such as anterior cruciate ligament reconstruction (ACLR). Restoring movement quality during sporting-type movements is important prior to return-to-sport (RTS) after ACLR. Alterations in movement quality during an array of functional tasks are common amongst ACLR patients at or near the time of RTS and are associated with worse outcomes after ACLR. The inability to correct movement issues prior to RTS is likely due to the use of incomplete programmes or a lack of volume and intensity of movement re-training programmes. Although most clinicians and researchers understand that re-training movement after ACLR is important (e.g., the ‘why’), there is often a disconnect with understanding the ‘how’ and ‘what’ of movement re-training post ACLR. The aim of this paper was to discuss factors relevant to movement dysfunction and re-training after ACLR and provide recommendations for clinicians to restore movement quality of patients after ACLR, prior to RTS. The paper recommends: (i) considering the factors which influence the expression of movement quality, which revolve around individual (e.g., neuromuscular, biomechanical, sensorimotor and neurocognitive factors), task-specific and environmental constraints; (ii) incorporating a three-staged movement re-training approach aligned to the ACLR functional recovery process: (1) addressing the neuromuscular and biomechanical and sensorimotor control factors which affect movement quality and motor learning, (2) including a progressive movement re-training approach to re-learn an array of functional tasks optimising coordination and motor learning (3) performing the final aspect of rehabilitation and movement training on the field, in realistic environments progressively simulating the sporting movement demands and environmental constraints; and (iii) effectively designing the movement programme for optimal load management, employing effective coach and feedback techniques and utilising qualitative movement analysis for transition between exercises, stages and for RTS.
... It is, however, important to understand the potential mechanisms responsible when considering adaptations in strength. An increase in strength but no increase in muscle mass may suggest adaptations occurred predominantly due to increased fascicle length, reduction in pennation angle [38] and neural adaptations [39]. Alternatively, an increase in strength and increase in muscle mass will likely lean towards increased muscle thickness and pennation angle as well as possible increases in fascicle length [38]. ...
Article
Full-text available
Background In-season competition and tournaments for team sports can be both long and congested, with some sports competing up to three times per week. During these periods of time, athletes need to prepare technically, tactically and physically for the next fixture and the short duration between fixtures means that, in some cases, physical preparation ceases, or training focus moves to recovery as opposed to progressing adaptations. Objective The aim of this review was to investigate the effect of training frequency on muscular strength to determine if a potential method to accommodate in-season resistance training, during busy training schedules, could be achieved by utilizing shorter more frequent training sessions across a training week. Methods A literature search was conducted using the SPORTDiscus, Ovid, PubMed and Scopus databases. 2134 studies were identified prior to application of the following inclusion criteria: (1) maximal strength was assessed, (2) a minimum of two different training frequency groups were included, (3) participants were well trained, and finally (4) compound exercises were included within the training programmes. A Cochrane risk of bias assessment was applied to studies that performed randomized controlled trials and consistency of studies was analysed using I² as a test of heterogeneity. Secondary analysis of studies included Hedges’ g effect sizes (g) and between-study differences were estimated using a random-effects model. Results Inconsistency of effects between pre- and post-intervention was low within-group (I² = 0%), and moderate between-group (I² ≤ 73.95%). Risk of bias was also low based upon the Cochrane risk of bias assessment. Significant increases were observed overall for both upper (p ≤ 0.022) and lower (p ≤ 0.008) body strength, pre- to post-intervention, when all frequencies were assessed. A small effect was observed between training frequencies for upper (g ≤ 0.58) and lower body (g ≤ 0.45). Conclusion Over a 6–12-week period, there are no clear differences in maximal strength development between training frequencies, in well-trained populations. Such observations may permit the potential for training to be manipulated around competition schedules and volume to be distributed across shorter, but more frequent training sessions within a micro-cycle rather than being condensed into 1–2 sessions per week, in effect, allowing for a micro-dosing of the strength stimuli.
... Together with the improved coordination patterns described above, peripheral and/or central recruitment of additional motor units and their higher discharge frequencies can be converted into strength increases (Henneman et al., 1965;Sale, 1988;Wakeling et al., 2002Wakeling et al., , 2006Wakeling et al., , 2012Jensen et al., 2005;Ansdell et al., 2020). ...
Article
Full-text available
The lactate threshold (LT) and the strongly related maximal lactate steady state workload (MLSSW) are critical for physical endurance capacity and therefore of major interest in numerous sports. However, their relevance to individual swimming performance is not well understood. We used a custom-made visual light pacer for real-time speed modulation during front crawl to determine the LT and MLSSW in a single-exercise test. When approaching the LT, we found that minute variations in swimming speed had considerable effects on blood lactate concentration ([La−]). The LT was characterized by a sudden increase in [La−], while the MLSSW occurred after a subsequent workload reduction, as indicated by a rapid cessation of blood lactate accumulation. Determination of the MLSSW by this so-called “individual lactate threshold” (ILT)-test was highly reproducible and valid in a constant speed test. Mean swimming speed in 800 and 1,500 m competition (S-Comp) was 3.4% above MLSSW level and S-Comp, and the difference between S-Comp and the MLSSW (Δ S-Comp/MLSSW) were higher for long-distance swimmers (800–1,500 m) than for short- and middle-distance swimmers (50–400 m). Moreover, Δ S-Comp/MLSSW varied significantly between subjects and had a strong influence on overall swimming performance. Our results demonstrate that the MLSSW determines individual swimming performance, reflects endurance capacity in the sub- to supra-threshold range, and is therefore appropriate to adjust training intensity in moderate to severe domains of exercise.
... Since it has been reported in the literature for neural mechanisms to be predominant in the early phase of training [25,26], and to contribute principally to force production from the second training week [27], and for hypertrophic processes to start contributing from the third or fourth weeks [26,28], a three-week period duration was established in order to meet the specific effect of heat upon mechanisms of force production beyond structural hypertrophy. ...
Article
Full-text available
The aim of this study was to evaluate the acute and adaptive effects of passive extreme heat (100 ± 3 °C) exposition in combination with a strength training protocol on maximal isometric handgrip strength. Fifty-four untrained male university students participated in this investigation. Twenty-nine formed the control group (NG) and 25 the heat-exposed group (HG). All the participants performed a 3-week isotonic handgrip strength training program twice a week with a training volume of 10 series of 10 repetitions with 45-s rest between series, per session. All the subjects only trained their right hand, leaving their left hand untrained. HG performed the same training protocol in hot (100 ± 3 °C) conditions in a dry sauna. Maximal isometric handgrip strength was evaluated each training day before and after the session. NG participants did not experience any modifications in either hand by the end of the study while HG increased maximal strength values in both hands (p < 0.05), decreased the difference between hands (p < 0.05), and recorded higher values than the controls in the trained (p < 0.05) and untrained (p < 0.01) hands after the intervention period. These changes were not accompanied by any modification in body composition in either group. The performance of a unilateral isotonic handgrip strength program in hot conditions during the three weeks induced an increase in maximal isometric handgrip strength in both hands without modifications to bodyweight or absolute body composition.
... Enhanced neural activation has long been argued to be a potential mechanism of resistance training strength adaptations in both young adults and older adults (Moritani and deVries, 1979;Sale, 1988;Folland and Williams, 2007;Adkins et al., 2006;Unhjem et al., 2021). Thus, we examined the relative changes in neural activation and muscle strength following exercise training. ...
Article
Background Older adults display wide individual variability (heterogeneity) in the effects of resistance exercise training on muscle strength. The mechanisms driving this heterogeneity are poorly understood. Understanding of these mechanisms could permit development of more targeted interventions and/or improved identification of individuals likely to respond to resistance training interventions. Thus, this study assessed potential physiological factors that may contribute to strength response heterogeneity in older adults: neural activation, muscle hypertrophy, and muscle contractility. Methods In 24 older adults (72.3 ± 6.8 years), we measured the following parameters before and after 12 weeks of progressive resistance exercise training: i) isometric leg extensor strength; ii) isokinetic (60°/sec) leg extensor strength; iii) voluntary (neural) activation by comparing voluntary and electrically-stimulated muscle forces (i.e., superimposed doublet technique); iv) muscle hypertrophy via dual-energy x-ray absorptiometry (DXA) estimates of regional lean tissue mass; and v) intrinsic contractility by electrically-elicited twitch and doublet torques. We examined associations between physiological factors (baseline values and relative change) and the relative change in isometric and isokinetic muscle strength. Results Notably, changes in quadriceps contractility were positively associated with the relative improvement in isokinetic (r = 0.37–0.46, p ≤ 0.05), but not isometric strength (r = 0.09–0.21). Change in voluntary activation did not exhibit a significant association with the relative improvements in either isometric or isokinetic strength (r = 0.35 and 0.33, respectively; p > 0.05). Additionally, change in thigh lean mass was not significantly associated with relative improvement in isometric or isokinetic strength (r = 0.09 and −0.02, respectively; p > 0.05). Somewhat surprising was the lack of association between exercise-induced changes in isometric and isokinetic strength (r = 0.07). Conclusions The strength response to resistance exercise in older adults appears to be contraction-type dependent. Therefore, future investigations should consider obtaining multiple measures of muscle strength to ensure that strength adaptations are comprehensively assessed. Changes in lean mass did not explain the heterogeneity in strength response for either contraction type, and the data regarding the influence of voluntary activation was inconclusive. For isokinetic contraction, the strength response was moderately explained by between-subject variance in the resistance-exercise induced changes in muscle contractility.
... There is also a difference in the recruitment of motor units depending on the activity of muscles. Motor units are recruited based on task-specific activation (Sale, 1988). For example, we use the muscles of the velum differently for swallowing than for articulation of speech sounds: As force is increased, larger axons are recruited, and larger units are recruited, increasing the strength of the muscle contraction (Lieber, 1992). ...
Article
Purpose The purpose of this clinical focus article was to identify clinical practice patterns of speech-language pathologists (SLPs) who use neuromuscular electrical stimulation (NMES) with the high-risk infants, specifically, the modality treatment parameters and physiological rationale. Method An online survey was disseminated to query use of NMES by licensed SLPs who routinely address swallowing habilitation in high-risk infants. Results Eleven of the 40 practicing SLPs who completed the survey indicated they have used NMES on neonates and infants. Most survey respondents reported not using NMES with infants. Of the SLPs who used this modality, over half reported they relied on clinical judgment for determination of NMES dose, frequency of treatments, electrode placement, and discharge determination. While SLPs acknowledged that little empirical evidence is available, those who used this modality indicated that the American Speech-Language-Hearing Association should support this modality in infants. Conclusions Reliance on clinical judgment, as indicated by SLPs who use NMES on high-risk infants, is not consistent with the evidence-based practice triad, which encourages the use of high-quality peer-reviewed published evidence to inform clinical decision-making. Additional basic and applied research is needed to support use of NMES as a therapeutic modality in infants.
... Aside from small improvements to the cardiovascular and respiratory systems, RT is effective at preventing unfavorable body composition shifts (i.e., increased body fat mass), improving insulin sensitivity (122), increasing bone mineral density, and most notably increasing muscle mass; all of which serve to improve whole-body health (76). RT induces significant neurological adaptations (90,234) that tend to occur early on within a RT program, which ultimately leads to greater force generation (i.e., strength and power). For instance, muscle strength (as assessed by single repetition maximum; 1RM) has been shown to increase from 10% to 175% over 8 to 26 weeks in men and women, young and old (5,156). ...
Article
Skeletal muscle is the organ of locomotion, its optimal function is critical for athletic performance, and is also important for health due to its contribution to resting metabolic rate and as a site for glucose uptake and storage. Numerous endogenous and exogenous factors influence muscle mass. Much of what is currently known regarding muscle protein turnover is owed to the development and use of stable isotope tracers. Skeletal muscle mass is determined by the meal- and contraction-induced alterations of muscle protein synthesis and muscle protein breakdown. Increased loading as resistance training is the most potent nonpharmacological strategy by which skeletal muscle mass can be increased. Conversely, aging (sarcopenia) and muscle disuse lead to the development of anabolic resistance and contribute to the loss of skeletal muscle mass. Nascent omics-based technologies have significantly improved our understanding surrounding the regulation of skeletal muscle mass at the gene, transcript, and protein levels. Despite significant advances surrounding the mechanistic intricacies that underpin changes in skeletal muscle mass, these processes are complex, and more work is certainly needed. In this article, we provide an overview of the importance of skeletal muscle, describe the influence that resistance training, aging, and disuse exert on muscle protein turnover and the molecular regulatory processes that contribute to changes in muscle protein abundance. © 2021 American Physiological Society. Compr Physiol 11:2249-2278, 2021.
... These disproportionate numbers are highlighted further by the previously reported low typical errors of 1.6-6% for vastus lateralis muscle thickness (Oranchuk et al., 2019(Oranchuk et al., , 2021. Also, since neural adaptations are the most evident adaptation during the early stages of training in untrained subjects (Moritani and Devries, 1979;Sale, 1988;Jessee et al., 2021), all their results of muscle thickness are entirely outlier (i.e., only 6 weeks of training). Finally, the Y-axis of FigA, B, D, and E range from −10 to 15 mm, whereas panel C ranges from −100 to 500 mm, leading us to believe that there was an error in data transcribing, log-transformation, or similar. ...
... Although some previous research has demonstrated that short-term (8-week) RET training with free weights or machines induces similar increases in muscle mass and strength (Schwanbeck et al., 2020), free weight usage has resulted in greater electromyography muscle activation (McCaw and Friday, 1994;Schwanbeck et al., 2009), and greater increases in circulating testosterone concentrations (Schwanbeck et al., 2020) than RET using machines. As most improvements in muscle strength during the first phases of training are due to neural adaptations rather than muscle hypertrophy (Moritani and deVries, 1979;Sale, 1988), it is not surprising that increases in muscle mass during short-term RET are similar with free weights and machines (Schwanbeck et al., 2020). However, the greater anabolic response and neural activation observed with free weight RET provide promising evidence that increases in strength and/or hypertrophy may be greater when using free weight RET than machines during longer-term training regimens. ...
Article
Full-text available
Muscle quality (MQ), defined as the amount of strength and/or power per unit of muscle mass, is a novel index of functional capacity that is increasingly relied upon as a critical biomarker of muscle health in low functioning aging and pathophysiological adult populations. Understanding the phenotypical attributes of MQ and how to use it as an assessment tool to explore the efficacy of resistance exercise training interventions that prioritize functional enhancement over increases in muscle size may have implications for populations beyond compromised adults, including healthy young adults who routinely perform physically demanding tasks for competitive or occupational purposes. However, MQ has received far less attention in healthy young populations than it has in compromised adults. Researchers and practitioners continue to rely upon static measures of lean mass or isolated measures of strength and power, rather than using MQ, to assess integrated functional responses to resistance exercise training and physical stress. Therefore, this review will critically examine MQ and the evidence base to establish this metric as a practical and important biomarker for functional capacity and performance in healthy, young populations. Interventions that enhance MQ, such as high-intensity stretch shortening contraction resistance exercise training, will be highlighted. Finally, we will explore the potential to leverage MQ as a practical assessment tool to evaluate function and enhance performance in young populations in non-traditional research settings.
... 26 Therefore, the low transfer and specificity of force performed in vertical jumps that are carried out at high speeds of execution, as seen in jump training, may not be detected in movements performed at a low speed of execution. 26,27 Studies that used assessments with different speeds of execution show that there is a strong correlation between vertical jump and the higher speeds of isokinetic tests. 14 The optimal relationship between AGO/ANT muscles of the knee (closer to 1) is related to a higher power in CMJ in volleyball players. ...
Article
Purpose: The authors aimed to compare the effects of 4 weeks jump versus complex training methods on lower limb muscle power and maximal isokinetic torque of knee extensors and flexors in elite male volleyball players. Methods: Sixteen male volleyball players were allocated into 2 groups, jump training (n = 8; 27.0 [5.7] y, 94.3 [7.6] kg) and complex training (with induction of postactivation performance enhancement, n = 8; 26.6 [3.6] y, 94.2 [6.3] kg). All individuals performed jump training 2 sessions/wk, and the complex group received induction training with postactivation performance enhancement and jump training. Results: After 4 weeks, an increase in countermovement jump height (jump: 49.0 [1.2] to 52.7 [2.1] cm and complex: 49.2 [1.1] to 53.3 [1.9] cm; P = .009) and power (jump: 29.5 [1.1] to 34.3 [1.4] W and complex: 30.4 [0.9] to 34.4 [1.08] W; P = .001) was observed without significant differences between groups and without significant group × time interaction (P > .05). Also, no significant difference was observed between and within groups for the isokinetic peak torque at low speeds (60 and 180°s), although total muscle work and knee extensor/flexor ratio increased from pretraining to posttraining at 300° seconds similarly in both groups. Conclusion: The findings indicate that jump performance and power, knee extensor/flexor ratio, and total muscle work increased after 4 weeks of jump and complex training. However, the inclusion of heavy resistance stimulus did not elicit any additional improvements in the vertical jump performance and isokinetic strength of elite volleyball players.
... Research by Alkjaer et al. [71] identified a significant increase in drop jump performance both in jump height achieved and the resultant RSI score following 4 weeks of intensive drop jump training, with muscle strength parameters unaffected. Thus, a more specific strength adaptation relative to the task may bring about a greater performance within rebound jumping tasks [72], highlighting the importance of training history and the nature of the sport competed in. Participants in the current review were from various sports and levels of competition, including volleyball [30], rugby [31,33,37,38,46,47], weightlifting [11,31], soccer [11,33], hockey [33], running [31], powerlifting [31], sprinting [33,34], tennis [35], basketball [11], and skill levels; collegiate [30,31,46], national [33,33], international [33,34], professional [37,47], semi-professional [38], and, novice/recreational [11,31,35,39]. ...
Article
Full-text available
Background Reactive strength index (RSI) is used frequently in the testing and monitoring of athletes. Associations with sports performance measures may vary dependent on the task but a literature synthesis has not been performed. Objectives The aim of this meta-analysis was to examine associations between RSI measured during rebound jumping tasks and measures of strength, linear and change of direction speed, and endurance performance. Methods A systematic literature search with meta-analysis was conducted using databases PubMed, SPORTDiscus, Web of Science, and Ovid. Inclusion criteria required studies to (1) examine the relationship between RSI and an independent measure of physical or sporting performance for at least one variable; and (2) provide rebound test instructions to minimise ground contact time and maximise displacement of the jump. Methodological quality was assessed using a modified version of the Downs and Black Quality Index tool. Heterogeneity was examined via the Q statistic and I². Pooled effect sizes were calculated using a random-effects model, with Egger’s regression test used to assess small study bias (inclusive of publication bias). Results Of the 1320 citations reviewed, a total of 32 studies were included in this meta-analysis. RSI was significantly and moderately associated with strength (isometric: r = 0.356 [95% CI 0.209–0.504]; isotonic: r = 0.365 [0.075–0.654]; pooled strength measures: r = 0.339 [0.209–0.469]) and endurance performance (r = 0.401 [0.173–0.629]). Significant moderate and negative associations were indicated for acceleration (r = − 0.426 [− 0.562 to − 0.290]), top speed (r = − 0.326 [− 0.502 to − 0.151]), and significant large negative associations were noted for change of direction speed (r = − 0.565 [− 0.726 to − 0.404]). Heterogeneity was trivial to moderate across all measures (I² = 0–66%), and significant for isotonic strength and change of direction speed (p < 0.1). Evidence of small study bias was apparent for both acceleration and change of direction speed (p < 0.05). Conclusions We identified primarily moderate associations between RSI and independent measures of physical and sporting performance, and the strength of these relationships varied based on the task and physical quality assessed. The findings from this meta-analysis can help practitioners to develop more targeted testing and monitoring processes. Future research may wish to examine if associations are stronger in tasks that display greater specificity.
... There are two possible origins of improvements in NHE performance by the players in the intervention part of our study: neural adaptation (a learning effect as a result of strength training in which adaptive changes occur within the nervous system) and muscle hypertrophy. It is widely considered that neural adaptation, rather than hypertrophy, plays the dominant role in increases in performance during the initial phase of strength training [34]. Moreover, it seems as if high-load strength training results in greater neural adaptations than low-load strength training [35]. ...
Article
Full-text available
There is evidence that a knee flexor exercise, the Nordic hamstring exercise (NHE), prevents hamstring injuries. The purpose of this study was therefore to develop, and to determine the reliability of, a novel NHE test device and, further, to determine the effectiveness of a 10-week low volume NHE program on NHE performance. Twenty female football (soccer) players, aged 16–30 years, participated in this study. From a kneeling position on the device, with the ankles secured under a heavy lifting sling, participants leaned forward in a controlled manner as far as possible (eccentric phase) and then returned to the starting position (concentric phase). A tape measure documented the forward distance achieved by the participants in cm. Participants completed three separate occasions to evaluate test-retest reliability. Additionally, 14 players performed a low volume (1 set of 5 repetitions) NHE program once weekly for 10 weeks. No significant test-retest differences in NHE performance were observed. The intra-class correlation coefficient was 0.95 and the coefficient of variation was 3.54% between tests. Mean improvement in the NHE performance test by the players following training was 22% (8.7 cm), p = 0.005. Our test device reliably measured NHE performance and is easy to perform in any setting. Further, NHE performance was improved by a 10-week low volume NHE program. This suggests that even a small dose (1 set of 5 repetitions once weekly) of the NHE may enhance NHE performance.
... This decrement in strength and power seen in patients with DPN can be further exacerbated in older adults who contend with age-related sarcopenia [14,121]. Engagement in regular RT has been demonstrated to be a primary intervention for increasing strength and power through neural adaptations across ages [122][123][124]. The use of heavy external loads, high velocity movements, and motor skill learning within RT aids in the increase of efferent neural drive through improved motor unit recruitment, motor neuron firing frequencies, motor unit synchronization, and the attenuation of antagonist co-activation [14,125]. ...
Article
Full-text available
Diabetic peripheral neuropathy (DPN) is the presence of symptoms and/or signs of peripheral nerve dysfunction in people with diabetes after the exclusion of other causes. It is associated with pain, paresthesia, sensory loss, muscle atrophy with fat infiltration, and muscular dysfunction typically starting distally in the feet and progressing proximally. Muscle deterioration within the leg and foot can lead to muscle dysfunction, reduced mobility, and increases the risk of disability, ulceration, and amputation. Exercise training is an established method for increasing the different components of physical fitness, including enhancing body composition and improving neuromus-cular strength. A number of experimental studies have utilized exercise training to treat various impairments associated with DPN, such as nerve conduction velocity, pain tolerance, and balance. However, the broad spectrum of exercise training modalities implemented and differences in target outcome measurements have made it difficult to understand the efficacy of exercise training interventions or provide appropriate exercise prescription recommendations. Therefore, the aims of this review were to (1) briefly describe the pathophysiology of DPN and (2) discuss the effects of exercise training interventions on sensorimotor, metabolic, and physical functions in people with DPN.
... Moreover, after 12 weeks, the groups that performed resistance training with high loads showed significant improvements in maximal strength compared to low load groups. As most studies assessed untrained individuals [11,[14][15][16][17]21,22,28,29,[42][43][44], it is possible to suggest that the early phases of resistance training were primarily impacted by enhancements in motor learning and coordination [49]. Therefore, low load training schemes might provide a sufficient stimulus to increase maximal strength. ...
Article
Full-text available
The load in resistance training is considered to be a critical variable for neuromuscular adaptations. Therefore, it is important to assess the effects of applying different loads on the development of maximal strength and muscular hypertrophy. The aim of this study was to systematically review the literature and compare the effects of resistance training that was performed with low loads versus moderate and high loads in untrained and trained healthy adult males on the development of maximal strength and muscle hypertrophy during randomized experimental designs. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (2021) were followed with the eligibility criteria defined according to participants, interventions, comparators, outcomes, and study design (PICOS): (P) healthy males between 18 and 40 years old, (I) interventions performed with low loads, (C) interventions performed with moderate or high loads, (O) development of maximal strength and muscle hypertrophy, and (S) randomized experimental studies with between-or within-subject parallel designs. The literature search strategy was performed in three electronic databases (Embase, PubMed, and Web of Science) on 22 August 2021. Results: Twenty-three studies with a total of 563 participants (80.6% untrained and 19.4% trained) were selected. The studies included both relative and absolute loads. All studies were classified as being moderate-to-high methodological quality, although only two studies had a score higher than six points. The main findings indicated that the load magnitude that was used during resistance training influenced the dynamic strength and isometric strength gains. In general, comparisons between the groups (i.e., low, moderate, and high loads) showed higher gains in 1RM and maximal voluntary isometric contraction when moderate and high loads were used. In contrast, regarding muscle hypertrophy, most studies showed that when resistance training was performed to muscle failure, the load used had less influence on muscle hypertrophy. The current literature shows that gains in maximal strength are more pronounced with high and moderate loads compared to low loads in healthy adult male populations. However, for muscle hypertrophy, studies indicate that a wide spectrum of loads (i.e., 30 to 90% 1RM) may be used for healthy adult male populations. Citation: Lacio, M.; Vieira, J.G.; Trybulski, R.; Campos, Y.; Santana, D.; Filho, J.E.; Novaes, J.; Vianna, J.; Wilk, M. Effects of Resistance Training
Article
Purpose: The purpose of this study was to compare the recovery response of one resistance training session (1TRS) vs. two resistance training sessions (2TRS) performed in 1 day, on upper body performance, muscle morphology and muscle soreness in trained men. Methods: Twenty-four resistance trained men were randomly assigned into a 1TRS group (N = 12; age = 25.0 ± 2.4 years; body mass = 87.6 ± 14.0 kg; height = 177.1 ± 4.9 cm) or into a 2TRS group (N = 10; age = 24.4 ± 1.6 years; body mass = 81.1 ± 5.6 kg; height = 176.6 ± 6.7 cm). 1TRS performed one training session involving eight sets of 10 reps at 70% of 1RM at the bench press, while 2TRS group divided the same training volume in two workouts, with a recovery time of 4 hr. Performance [bench press throw power (BTP) and isometric bench press (IBP)] and muscle thickness of pectoralis major (PECMT) were assessed at baseline (BL), 15-min, 24-hr and 48-hr post-exercise. Results: Training intensity was significantly higher in 2TRS compared to 1TRS (p < .001). Faster recovery rates were detected for BTP (p = .039) and PECMT (p = .05) in 2TRS compared to 1TRS. Both BTP and PECMT were significantly more affected (p < .05) in 1TRS than in 2TRS at 24 h. Conclusions: Results indicate that the recovery process may be accelerated by splitting a high resistance training volume into two different training sessions performed in 1 day.
Article
Full-text available
This narrative review deals with the topic of strength training in swimming, which has been a controversial issue for decades. It is not only about the importance for the performance at start, turn and swim speed, but also about the question of how to design a strength training program. Different approaches are discussed in the literature, with two aspects in the foreground. On the one hand is the discussion about the optimal intensity in strength training and, on the other hand, is the question of how specific strength training should be designed. In addition to a summary of the current state of research regarding the importance of strength training for swimming, the article shows which physiological adaptations should be achieved in order to be able to increase performance in the long term. Furthermore, an attempt is made to explain why some training contents seem to be rather unsuitable when it comes to increasing strength as a basis for higher performance in the start, turn and clean swimming. Practical training consequences are then derived from this. Regardless of the athlete’s performance development, preventive aspects should also be onsidered in the discussion. The article provides a critical overview of the abovementioned key issues. The most important points when designing a strength training program for swimming are a sufficiently high-load intensity to increase maximum strength, which in turn is the basis for power, year-round trength training, parallel to swim training and working on the transfer of acquired strength skills in swim training, and not through supposedly specific strength training exercises on land or in the water.
Article
Full-text available
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.
Article
Objective to provide evidence for the effects of whole-body electromyostimulation (WB-EMS) on health-related outcomes compared to the effects of minimal or non-intervention for older people in the short/medium/long term. Data sources seven databases (MEDLINE, Embase, CENTRAL, CINAHL, Scopus, SPORTDiscuss and Web of Science) were electronically searched in April 2020 and updated in March 2021. Study selection included studies were randomized controlled trials (RCTs) involving WB-EMS that assessed effects on health-related outcomes, risks and adverse events in older people (>60 years). Data extraction the following data were obtained: author and publication year, follow-up, detailed information of older characteristics, current parameters/intensity and outcomes. Data synthesis a random effects model was used with effect size reported as SMD. Statistical heterogeneity was assessed using the I² test. Results 13 RCTs met the eligibility criteria. Meta-analysis found: large effects of WB-EMS on reducing sarcopenia Z-score (ES: 1.44[-2.02: 0.87] p= <.01) and improving isometric strength leg extensors (ES:0.81[0.41:1.21] p= <.01) at medium and long-term, respectively. Moderate effects of WB-EMS on improving handgrip strength (ES:0.58[0.23:0.92] p= <.01) and habitual gait speed (ES:0.69[0.31:1.07] p= <.01) at medium-term and improving appendicular skeletal muscle mass (ES:0.69[0.30:1.09] p= <.01) at long-term. Non-significant effect of WB-EMS on waist circumference (p = .17) and triglycerides (p = .20) at medium-term. Non-significant effects of WB-EMS on improving creatine kinase concentrations, C-reactive protein, and interleukin 6 at medium-term. Conclusions This review provides further evidence for significant, moderate to large effect sizes of WB-EMS on sarcopenia, muscle mass and strength parameters, but not on waist circumference and triglycerides. Systematic review registration PROSPERO database no. CRD42019134100.
Article
Background: Weakness and disuse of intrinsic foot muscles contributes to dysfunction in foot and toe alignment and sensory input, which may lead to instability and falls in older adults. The aim of this systematic review was to report the effects of intrinsic foot muscle strengthening (IFMS) interventions on functional mobility in adults aged ≥65 years. Methods: A systematic review was performed with searches from December 2019-February 2021 using MEDLINE, CINAHL, SPORTDiscus, Rehab and Sports Medicine Source, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials. Additional sources were sought using reference scanning. Eligible sources analyzed adults aged ≥65 years (n = 1674) who were ambulatory, used a functional mobility outcome measure, and contained foot and ankle interventions that included IFMS. Literature studies regarding neurological, vestibular, cognitive, amputation, or post-surgical conditions were excluded. Studies that did not specify intrinsic foot muscle involvement were excluded. Two authors extracted relevant studies and appraised them using the Physiotherapy Evidence Database (PEDro) scale. Results: A total of 1420 articles were screened for relevance, and 16 were extracted. Five additional sources were obtained through reference scanning. Nine articles were eligible for review. PEDro scores ranged from 3 to 7 (out of 10), indicating "fair" quality of evidence. Heterogeneity of methods and data did not allow for statistical comparison. Themes extracted from sources were types of intrinsic foot strengthening interventions and parameters; outcomes on falls, balance, functional mobility; and subjective reports regarding functional mobility. Conclusion: Evidence reviewed was of fair quality. IFMS interventions contributed to improvements in strength, balance, mobility, and possibly reduced fall risk. There was little effect on gait. Subjective reports indicate a possible mechanism for improved mobility may be from increased proprioception and sensation.
Chapter
Full-text available
In conventional Ayurveda and Unani frameworks of medication, the foundations of Indian Ginseng or Ashwagandha have a long history of utilization as an adaptogen. Ashwagandha (Withania somnifera (L.) Dunal) is an individual from the Solanaceae group of plants. Keeping up with general prosperity and improvement of essentialness has been the essential significance of this "Rasayana". In spite of the fact that the idea to be valuable as a restorative spice in Ayurveda and sold in numerous nations as a dietary enhancement, there is lacking logical proof that it is protected or successful for treating any infection.
Article
Introduction Neuromuscular electrical stimulation (NMES) is used by athletes to improve muscle performance. However, evidence on the use of NMES in long distance runners is scarce. As such, this study aimed to evaluate the effects of NMES on the muscle torque and sports performance of long-distance recreational runners. Methods This was a blinded randomized controlled trial. Data from 30 volunteers were analyzed. Participants were randomly allocated to an experimental (n = 15) or control group (n = 15). The experimental group was submitted to running training (RT) and a strengthening protocol with NMES (1 kHz, modulated in 2ms bursts, 50Hz modulated burst frequency and 10% duty cycle, 15 minutes totaling 18 contractions per sessions) for 6 weeks, with 3 sessions per week, while controls were submitted to RT alone. The following variables were analyzed: peak isometric (ISO), concentric (CON), and eccentric (ECC) torque of the quadriceps muscle in voluntary contractions, ventilatory anaerobic thresholds (VATs), maximal oxygen uptake (VO2max), and oxygen cost of transport (OCT). Results The NMES group obtained higher values of ISO, 21.04% (p = 0.001), CON, 21.97% (p = 0.001) and ECC, 18.74% (p = 0.001) peak torque and VAT1, 9.56% (p = 0.001), as well as a statistically significant improvement in oxygen cost of transport at VAT1 when compared to controls (p = 0.001). Conclusion NMES was effective in improving peak isometric, concentric and eccentric quadriceps muscle torque, in addition to being an interesting resource for enhancing sports performance in long-distance recreational runners and future clinical trials should be performed to compare the use of NMES to different forms of training over longer training periods.
Chapter
Facing a chronic ankle instability, an early neuromuscular reprogramming is mandatory to restore the active joint protection system. Specifically, it means strengthening the ankle stabilizing muscles (evertor) associated with proprioceptive work. There is a lack of specificity of the commonly used tools as the restoration of proprioceptive acuity needs to improve the proactivation of the fibular muscles with strengthening in weight-bearing condition. A rearfoot destabilization element combined to a dynamic work capacity in locomotion will provide capacity to solicit proactivation and to resort to proactivation fibular strategies. The advantages of the specific Myolux tool are exposed, and a proposal of its integration in a post-operative protocol following lateral ankle ligamentoplasty is developed.
Chapter
Ankle sprains are the most common injuries sustained during sporting activity. In the UK, there are approximately 5600 incidences per day, accounting for between 3% and 5% of all Emergency Department attendances [1]. In the USA, the figures are 30,000 per day or 2 million per year [2, 3]. The actual incidence of ankle sprain is, of course, much higher than this as it is estimated that as many as 55% of patients do not seek evaluation or treatment from a healthcare professional [4]. In a Systematic Review and Meta-Analysis of Prospective Epidemiological Studies, Doherty et al. [5] found that female sex, lower age and athletes competing in indoor and court sports are the subgroups most at risk of ankle sprain. The majority of ankle sprains will recover without surgery, but around 20% of patients will go on to develop chronic ankle instability [6] and up to 34% will sprain their ankle again within 3 years of the initial injury [7]. There is no correlation between the initial severity of the sprain and the subsequent development of chronic instability [8]; therefore, other factors are responsible for the outcome of these injuries. Without adequate diagnosis and treatment, ankle injuries may lead to chronic instability, osteoarthritis and other permanent sequelae [9–11].
Article
Neural and morphological adaptations combine to underpin the enhanced muscle strength following prolonged exposure to strength training, although their relative importance remains unclear. We investigated the contribution of motor unit (MU) behaviour and muscle size to submaximal force production in chronically strength-trained athletes (ST) vs. untrained controls (UT). Sixteen ST (age, 22.9±3.5 yr; training experience, 5.9±3.5 yr) and fourteen UT (age, 20.4±2.3 yr) performed maximal voluntary isometric force (MViF) and ramp contractions (at 15, 35, 50, 70%MViF) with elbow flexors, whilst high-density surface EMG (HDsEMG) was recorded from the biceps brachii (BB). Recruitment thresholds (RT) and discharge rates (DR) of MUs identified from the submaximal contractions were assessed. The neural drive-to-muscle gain was estimated from the relation between changes in force (ΔFORCE, i.e. muscle output) relative to changes in MU DR (ΔDR, i.e. neural input). BB maximum anatomical cross-sectional area (ACSA MAX ) was also assessed by MRI. MViF (+64.8% vs. UT, P<0.001) and BB ACSA MAX (+71.9%, P<0.001) were higher in ST. Absolute MU RT was higher in ST (+62.6%, P<0.001), but occurred at similar normalized forces. MU DR did not differ between groups at the same normalized forces. The absolute slope of the ΔFORCE-ΔDR relationship was higher in ST (+66.9%, P=0.002), whereas it did not differ for normalized values. We observed similar MU behaviour between ST athletes and UT controls. The greater absolute force-generating capacity of ST for the same neural input, demonstrates that morphological, rather than neural, factors are the predominant mechanism for their enhanced force generation during submaximal efforts.
Article
Full-text available
Purpose: This study was aimed at comparing the effects of TheraBand and theratube eccentric exercises on quadriceps muscle strength in young adults. Methods: Thirty young adults (19 females, 11 males) participated in this pretest-posttest experimental study. Participants were randomly assigned to one of the two groups: TheraBand and theratube groups. They received the training intervention 3 times a week for 4 weeks (12 sessions) with progression after 2 weeks. Maximum eccentric quadriceps strength was assessed using the Biodex isokinetic dynamometer system. Additionally, quadriceps muscle mass was measured using a tape. Results: Both groups showed a significant improvement in the peak torque of the eccentric isokinetic quadriceps' strength after weeks 2 and 4. Strength change in the quadriceps was nonsignificant in the theratube group compared to the TheraBand group after 4 weeks of training (p < 0.05). There was no increase in muscle mass during the 4 weeks of training in any group (p > 0.05). Conclusion: Both the TheraBand and theratube are equally effective in the strengthening of the quadriceps muscle in young adults. Therefore, either the TheraBand or theratube may be used according to the availability and feasibility of the subjects for training intervention.
Article
This study investigated whether an increase in toe flexor strength influenced postural control during static upright standing after 12 weeks of multicomponent exercise training in healthy young men. Twelve men (18-23 yrs) performed multicomponent exercise 3 days per week for 12 weeks. Twelve additional age-matched men were recruited for the untrained control group. The multicomponent exercise training consisted of strengthening and balance exercises for the foot and leg muscles. Toe flexor strength, foot arch height and postural control were assessed before, during, and after exercise training. Postural control was evaluated using the path of the centre of pressure, which was obtained with a force plate under three standing conditions: double-leg standing with eyes open, double-leg standing with eyes closed, and single-leg standing with eyes open. The dominant leg was used for single-leg standing. After exercise training, toe flexor strength increased by approximately 32% (p < 0.01), whereas the foot arch height did not change. The centre of pressure variables during double-leg standing did not change after exercise training; however, these variables decreased during single-leg standing. None of the variables in the control group changed after exercise training. The relative increase in toe flexor strength was not correlated with the relative improvement in the centre of pressure variables during single-leg standing after 12 weeks of exercise training (total length, r = 0.1734; mean velocity, r = 0.1734; sway area, r=-0.1372). These findings suggest that increased toe flexor strength has no significant effect on static postural control ability after exercise training in young men.
Article
Résumé La musculation à haute intensité en télé-rééducation présente de nombreuses plus-values pour améliorer la qualité de vie de personnes atteintes de paralysie cérébrale. Le 17 mars 2020 a débuté le « confinement de la population » lié à la COVID-19 en France. Cette mesure sanitaire a remis en cause le déroulement habituel des séances de rééducation. Pour s’adapter à ce contexte, des séances de télé-rééducation synchrones et asynchrones essaient de se mettre en place rapidement afin que les personnes atteintes de paralysie ne perdent pas les bénéfices de leur accompagnement et préservent leurs capacités motrices. Cette pratique à distance, bien développée dans d’autre pays, est une découverte récente en France. Elle reste d’actualité et devrait se pérenniser comme nouvel arsenal thérapeutique dans le cas où son indication reste pertinente. Nous aborderons d’abord les intérêts et les limites de la télé-rééducation. Puis, les origines de la faiblesse musculaire des personnes atteintes de paralysie cérébrale seront évoquées. Ensuite, les multiples plus-values de la musculation à haute intensité seront développés. Enfin, nous montrerons que l’utilisation de cette rééducation novatrice, qui permet réellement d’améliorer la qualité de vie de cette population, est particulièrement intéressante en télé-rééducation.
Article
Human physiology is likely to have been selected for endurance physical activity. However, modern humans have become largely sedentary, with physical activity becoming a leisure-time pursuit for most. Whereas inactivity is a strong risk factor for disease, regular physical activity reduces the risk of chronic disease and mortality. Although substantial epidemiological evidence supports the beneficial effects of exercise, comparatively little is known about the molecular mechanisms through which these effects operate. Genetic and genomic analyses have identified genetic variation associated with human performance and, together with recent proteomic, metabolomic and multi-omic analyses, are beginning to elucidate the molecular genetic mechanisms underlying the beneficial effects of physical activity on human health. Regular physical activity reduces the risk of chronic disease and mortality, but the mechanisms underpinning this protective effect are poorly understood. Here, Kim et al. review candidate genes and pathways implicated in human performance by genetic, genomic and multi-omic studies.
Article
Full-text available
Although appendicular skeletal muscle mass (ASM) and handgrip strength (HGS) are key components of sarcopenia, their underlying biological mechanisms remain poorly understood. We aimed to investigate associations of circulating biomarkers with ASM and HGS in middle-aged black South Africans. This study consisted of 934 black South Africans (469 men and 465 women, aged 41–72 years) from the Middle-aged Soweto cohort. Linear regression models were used to examine relationships between 182 biomarkers (measured with proximity extension assay) and dual-energy X-ray absorptiometry-measured ASM and dynamometer-measured HGS. Age, height, sex, smoking, alcohol, food insecurity, physical activity, visceral adipose tissue, HIV and menopausal status were included as confounders. Regression models showing sex-interactions were stratified by sex. The Benjamini–Hochberg false discovery rate (FDR) was used to control for multiple testing, and FDR-adjusted P values were reported. In the total sample, 10 biomarkers were associated with higher ASM and 29 with lower ASM (P < 0.05). Out of these 39 biomarkers, 8 were also associated with lower HGS (P < 0.05). MMP-7 was associated with lower HGS only (P = 0.011) in the total sample. Sex-interactions (P < 0.05) were identified for 52 biomarkers for ASM, and 6 for HGS. For men, LEP, MEPE and SCF were associated with higher ASM (P < 0.001, = 0.004, = 0.006, respectively), and MEPE and SCF were also associated with higher HGS (P = 0.001, 0.012, respectively). Also in men, 37 biomarkers were associated with lower ASM (P < 0.05), with none of these being associated with lower HGS. Furthermore, DLK-1 and MYOGLOBIN were associated with higher HGS only (P = 0.004, 0.006, respectively), while GAL-9 was associated with lower HGS only (P = 0.005), among men. For women, LEP, CD163, IL6, TNF-R1 and TNF-R2 were associated with higher ASM (P < 0.001, = 0.014, = 0.027, = 0.014, = 0.048, respectively), while IGFBP-2, CTRC and RAGE were associated with lower ASM (P = 0.043, 0.001, 0.014, respectively). No biomarker was associated with HGS in women. In conclusion, most biomarkers were associated with ASM and not HGS, and the associations of biomarkers with ASM and HGS displayed sex-specificity in middle-aged black South Africans. Proteomic studies should examine ASM and HGS individually. Future research should also consider sexual dimorphism in the pathophysiology of sarcopenia for development of sex-specific treatment and diagnostic methods. Introduction
Article
Full-text available
We examined the electromyographic (EMG) activity of two human elbow-flexor muscles, biceps brachii and brachioradialis, during isometric contractions. The task required subjects to match the EMG level of one of the muscles (the control muscle) to one of four target levels (5, 10, 15, or 20% of maximum) at various elbow angles. A new technique was developed for the target-matching task. The activity of the other muscle (the test muscle) was simultaneously recorded during the task. For the notion of flexor equivalence to be supported, the EMG levels for the two muscles should have covaried. This was not the case. The results revealed three features: (1) while the control-muscle EMG remained constant across joint angles, the test-muscle EMG varied with joint angle, and the trend of this variation differed among subjects; (2) in nine out of ten subjects the trend of test-muscle EMG variation with joint angle was reversed when the other muscle served as the test muscle; and (3) the test-muscle EMG associated with the four target levels was subject-, muscle-, and angle-dependent. These results caution against the generalization of the flexor equivalent concept to isometric conditions. In particular, the activity of one muscle is not a reliable indicator of the activity of other muscles subserving the same joint action.
Article
The force of maximal voluntary contraction (MVC) was compared during extension of one leg alone and during simultaneous extension of both legs. In 6 subjects MVC of two leg extension was 75 + 3.6 (S.E.) % of the sum of the single one leg MVC. This may indicate a reduced muscle fibre involvement during two leg extension as compared with one leg extension. We investigated the possibility that either red (type I) or white (type II) muscle fibre recruitment was restricted during two leg extension. The neuromuscular transmission in the two types of fibres was partially blocked with d-tubocurarine (dtc) or decamethonium (C10) for either type 1 or II, respectively. In 5 subjects receiving dtc the ratio between the reduced two leg and one leg extension forces (75 ± 2.3%) did not change. During administration of C10, however, this ratio decreased by 16 ± 3.1 %. Partial blocking with dtc caused a two component curve during tension development with a first maximum at 0.22 s, and another maximum at 1.03 s of a 3 s attempt to reach MVC. During partial blocking with C10 the first maximum disappeared indicating human fast twitch fibres to be blocked by C10. Thus, partial blocking with C10 results in muscle contractions where a relatively large amount of type I muscle fibres are contributing to the force developed. The experiment suggests that type I fibre recruitment is restricted during severe static exercise in normal muscles. Furthermore, it demonstrates that fibre recruitment can vary in the same muscle function performed with one leg or two legs.
Article
The motoneuron part of this review deals with the changes in recruitment and firing rates of the motor unit types upon changes from a physically inactive life to endurance or strength training. The muscle fibers react to prolonged exercise by adaptation to a higher level of performance. A matter of discussion is the prerequisites for a transformation between the basic muscle fiber types, slow twitch and fast twitch, during voluntary (transsynaptic) activity, which is demonstrated after artificial nerve stimulation. The review includes current knowledge of muscle fiber transformation as an adaptive response to increased usage either by electrical stimulation or by transsynaptic neuronal activity. The metabolic adaptation related to increased endurance is reviewed with special reference to effects on muscle fibers. The increase in strength as a result of high resistance training is mainly the result of increased muscle cross-section. Whether this is solely the result of an increase in size of individual fibers or an increased fiber number is a controversial matter.
To investigate training-induced changes in neuromuscular performance under voluntary and reflex contractions, 11 male subjects went through heavy resistance (high loads of 70–120% of one maximum repetition) and 10 male subjects through explosive type (low loads with high contraction velocities) strength training three times a week for 24 weeks. A large increase (13.9%,p<0.01) in voluntary unilateral maximal knee extension strength with only slight and insignificant changes in time of isometric force production were observed during heavy resistance strength training. Explosive type strength training resulted in a small insignificant increase in maximal strength but in considerable shortening (p<0.05) in the time of force production. A significant increase (p<0.05) noted in the averaged maximal integrated electromyogram (IEMG) of the knee extensors during heavy resistance strength training correlated (p<0.01) with the increase in maximal strength. No changes were noted during training in reflex time components, but significant decreases (p<0.05) occurred in the peak-to-peak amplitudes of the reflex electromyograms (EMG) in both groups. The individual changes during training in the reflex EMG/force ratio were related (p<0.01) to the respective changes in IEMG/force ratio in voluntary contractions. The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.
Some normal human subjects show definite synchronization of the motor units in hand muscles (i.e., the impulses from two or more motor units coincide in time more frequently than expected for independent random processes). Subjects who show synchronization tend to use their hands to exert large, brief forces, either in their work (e.g., manual laborers) or recreational activities (e.g., weightlifters). In this study all seven weightlifters examined showed a significant degree of synchronization. Furthermore, after 6 weeks of using the first dorsal interosseus muscle of the hand to exert maximal, voluntary contractions, the level of synchronization increased substantially in four control subjects, and the average level became significantly different from zero. Weightlifters also showed greater late reflex responses than control subjects, but no significant difference in earlier spinal reflexes. Two late reflex waves are described which probably involve fast pathways to and from motor cortes. We suggest that supraspinal connections from motor cortex directly to spinal motoneurons may be enhanced as a result of training to the point where they produce a significant synchronization of motor units during steady, voluntary contractions.
One-leg exercise of 5 weeks duration in 10 healthy middleaged women resulted in a significant increment of muscle force in the exercising leg and in a less, but at some angular velocities also significant, increase in the nonexercising leg. The thickness of subcutaneous tissue measured by ultrasound and skinfold caliper decreased, while muscle thickness increased in the exercising leg only. The increased thickness of muscle tissue was associated with an increase in the relative number and relative fiber area of type II fibers in the exercising leg. The mean fiber area of type IIB fibers increased significantly as well as the activity of lactate dehydrogenase and myokinase. The decrease of thickness of subcutaneous adipose tissue was not associated with a significant decrease in fat cell size and was probably due to geometrical factors secondary to hypertrophy of the underlying muscle. It is concluded that the relationship between lean and fat components of the human thigh is significantly influenced by changes in the activity of the thigh skeletal muscles, but a local dynamic strength training program can hardly be used for local emptying of the fat depot over the exercising muscles.
Article
Progressive strength training was performed 3 times a week for 8 weeks by 14 male students (19-31 yrs.). The training program consisted mainly of dynamic exercises for the leg extensors with maximal or close to maximal loads. The training caused significant improvements in dynamic and isometric strength. One repetition maximum in squats increased with 67%, Sargent jump with 22%, and maximal voluntary isometric contraction (MVC) with 13%, respectively. Body weight and leg muscle circumferences remained unchanged after training, whereas total body potassium, lean body mass and calculated total muscle mass increased, suggesting a change in body composition with training. Muscle biopsies were obtained from vastus lateralis for fibre analyses and determination of enzyme activities. There were no changes in muscle fibre composition or fibre area with training. The activities of Mg2+ stimulated ATPase, creatine phosphokinase and phosphofructokinase remained unchanged, whereas myokinase activity was increased after training from (1.41 to 1.52 moles x 10(-4) x g-1 x min-1, p less than 0.05). After training significant correlations (p less than 0.01) were demonstrated between Mg2+ stimulated ATPase activity and % fast twitch fibres (% FT) (r = 0.67), as well as between myokinase activity and % FT (r = 0.86).
Article
Activity of single motor units was recorded with highly-selective electrodes from the masseter muscle in intact man with normal dentition. The inter-occlusal isometric force was simultaneously recorded. The fractional contribution of the masseter to jaw clenching estimated from integrated EMG and isometric tetanic tension was about 0.33 both in slow or brisk voluntary clenches. The recruitment order of motor units raises problems in brisk contractions because the spikes of motor units cannot be directly related in time to the steeplyincreasing force record. A method was used which relates threshold activation of any unit to the peak force of brisk contractions. The rank ordering of masseter motor units was identical in the tonic reflex to chin vibration, in slow and brisk voluntary clenches. No evidence was found for any reversal of the recruitment order over a wide range of contraction speeds.
Isometric and dynamic strength and endurance of knee extensors were tested in 18 young males. The relative composition of slow (ST) and fast twitch (FT) fibers in the vastus lateralis muscle was registered from needle biopsies. Thigh muscle volume was evaluated from ultrasonic measurements. Six subjects served as controls, six trained with 50%, and six with 80% dynamic strength three times per week for 7 weeks with 20 and 12 repetitions per session, respectively. The training load was adjusted to the increases in strength observed during training. Dynamic strength increased by 42.3% in the 80% group (p< 0.01). In the control group and 50% group no significant increases were observed. Dynamic endurance: Controls showed no change. There was an over-all increase in the 50% group, while the 80% group only increased dynamic endurance for heavier loads. Isometric strength and endurance and fiber composition did not change in any group. In the 50% group the area of FT-realtive to ST-fibers increased 12.4% (p>0.05). Dynamic strength relative to muscle cross section increased by 30% in the 80% group (p<0.01) positively correlated to relative content of FT fibers. The present results confirm the specificity of training and indicate that a high content of FT fibers is a prerequisite for a successful strength training.
Article
The integrated electromyogram of the first dorsal interosseous muscle in normal humans presents a brief early burst in voluntary ballistic abduction of the index finger. Unexpected decrease in torque load does not change the burst. By contrast, in fast ramp abduction with a time-to-peak of 0.5 second, the electromyographic activity is fairly continuous up to the peak displacement, and it is silenced with a delay of 50 msec by unexpected unloading. Thus fast ramp, but not ballistic, voluntary contractions are under current long loop control from proprioceptive input. In a second set of experiments, the analysis of single motor unit potentials with highly selective electrodes in interosseous muscle indicated that ballistic thresholds are smaller than ramp thresholds under either isotonic or isometric conditions. However, the recruitment rank of the motor units was identical in finger abductions carried out in either ramp or ballistic modes.
Monozygous twin pairs (two female and four male) were used in a strength training study so that one member of each pair served as training subject (TS) and the other members as nonexercising controls (CS). TS trained four times a week for 12 weeks with maximal isometric knee extensions of the right leg. The parameters studied included muscle strength, endurance time, electromyographic activity, and activities of several key enzymes in nonoxidative an oxidative muscle metabolism. The results disclosed that in addition to a 20% increase in isometric knee extension strength in the trained leg of TS, an average increase of 11% was observed in strength of TS untrained leg. CS did not demonstrate any change in muscle strength. Training also included an improvement in the maintenance of a static load of 60% of the pretraining maximum. Increase in the maximum integrated electromyographic activity (IEMG) of the rectus femoris muscle occurred concomitantly with the knee extension strength. Traning also caused reduction in the IEMG/tension ratio at submaximal loads indicating a more econimical usage of the rectus femoris muscles. Muscle biopsies taken from the vastus lateralis muscle showed that the enzyme activities of MDH, SDH, and HK were higher, and LDH and CPK lower in the trained leg as compared to the nontrained control leg of TS or to the values of the untrained member of the twin pair. It is concluded that isometric strength training as used in the present study can cause increased recruitment of the availabel motor unit pool, improved efficiency at submaximal loads, and surprisingly also enchancement of the oxidative metabolism in the muscle.
Article
In cats anesthetized with alpha-chloralose, different populations of motor units in soleus, plantaris, and medial gastrocnemius muscles were stimulated in rotation through surgically divided groups of ventral roots. As a result, smooth muscular contractions were obtained at low frequencies of rotary stimulation, and maximal tetanic tensions were induced at frequencies within the upper range of voluntary contractions. The frequencies necessary to induce maximal tetanic contractions were lower for slow-twitch muscles than for fast-twitch muscles. It is speculated that the primary benefit resulting from asynchronous stimulation of the muscles is in the engagement of the tendon, which permits motor units to exert their tension without having to overcome a major portion of the elastic damping.
Article
The training effects of static and dynamic exercise programs on the firing patterns of 450 single motor units (SMU) in the human tibialis anterior muscle were investigated. In a six week program, the static group (N = 5) participated in daily high intensity, short duration exercises (isometric) while the dynamic group (N = 5) participated three times weekly in low intensity, moderate duration endurance exercises (isotonic). The control group (N = 4) did not participate in an exercise program. Pre- and posttest SMU firing patterns were recorded by means of 26 gauge tygon coated monopolar needle electrodes. In order to assess the degree of impersistence of periodicity of motor unit firing, an interspike interval (ISI) longer than 260 msec was defined as a lapse in motor unit firing. This value is >5 S.D. longer than the mean ISI at onset of firing for motor units in tibialis anterior. An individual ratio (ILU) of normal ISIs to lapses for each SMU three minute recording run and the mean ratio for each subject (MLR) were calculated. Significant differences were found between MLR pre- and posttest values for both groups (p<0.05). These results indicate that changes in motor unit firing can be produced by specific exercise programs; high intensity, short duration and low intensity, long duration exercises producing firing rates more and less variable than normal respectively.
Article
In 2 earlier studies (Thorstensson et al. 1976 a and b) the effect of 8 weeks of heavy progressive strength training were investigated in 22 male students of physical education. Briefly, the results showed that the training regimen caused a large gain in strength performance and an increase in muscle mass, but only minor changes in muscle fibre characteristics, enzyme activities and EMG. One subject (E.G.) continued training after the initial 8 weeks and was reexamined 5 mth later along with another subject (A. M.) who had not been participating in any strength training for the corresponding period of time. This paper reports results from strength tests, anthropometric measurements and muscle fibre analyses for these 2 subjects before and after the initial training period as well as after the additional 5 mth.
Article
The effects of an 8 weeks period of systematic progressive strength training on the EMG activity of the leg extensor muscles (vastus lateralis and rectus femoris) were investigated in 8 healthy male subjects (22-31 yrs). After training there were indications (n.s.) of a decline in integrated EMG (IEMG) during maximal isometric knee extension as well as in the IEMG vs isometric force relationship. The averaged motor unit potential (AMUP) did not demonstrate any significant changes due to the strength training regimen. In conformity with earlier findings no or only minor alterations were observed in anthropometrics, muscle enzyme activities and fibre composition. The fibre area ratio indicated a specific effect of the training stimuli on the fast twitch muscle fibres. Thus, EMG-analyses, as employed in the present study, did not provide any conclusive additional explanation as to the mechanisms behind the well established gains in muscle strength performance induced by the applied strength training program.
Article
The projection of C3-C4 propriospinal neurones (PNs) to alpha-motoneurones of forelimb muscles has been analysed with the aid of antidromic stimulation of the ascending branch of the PNs to the lateral reticular nucleus (LRN). A single stimulus of 500 microA applied in the caudo-dorsal part of the LRN evoked a maximal or greater than 90% maximal monosynaptic EPSP in the motoneurones. Systematic mapping of EPSPs evoked by stimulation of 500 microA in and around the LRN revealed that at this strength there was hardly any co-activation of a medial system (Peterson et al. 1979) which evoked small monosynaptic EPSPs with shorter latency and faster time course. The LRN EPSP amplitude was positively correlated with the homonymous group Ia EPSP amplitude, the input resistance and the afterhyperpolarization (AHP) duration. It is therefore postulated that the LRN EPSP amplitude is correlated with motor unit type (Burke 1967, 1968; Burke et al. 1973) with the largest EPSPs in slow (S), the smallest in fast, fatiguable (FF) and possibly intermediate sized in fast, fatigue resistant (FR) units. There was only a small difference in latency of the LRN EPSP in fast and slow motoneurones, while the time course was considerably slower in the latter. It is suggested that slow motoneurones receive projection both from fast and slowly conducting PNs but fast motoneurones mainly from fast PNs. Comparison of the disynaptic pyramidal EPSPs and the LRN EPSPs revealed a positive correlation, but the amplitude ratio pyramidal EPSP: LRN EPSP was smaller in slow than in fast motoneurones. A negative correlation was found between this amplitude ratio and the latency of the disynaptic pyramidal EPSP. It is suggested that this correlation reflects the excitability level in the PNs and that low excitability is due to inhibition of the PNs.
Synergistic behaviour of triceps surae muscles (medial gastrocnemius-MG, lateral gastrocnemius-LG, soleus-SOL) during sustained submaximal plantarflexions was investigated in this study. Six male subjects were asked to sustain an isometric plantar flexor effort to exhaustion at two different knee angles. Exhaustion was defined as the point when they could no longer maintain the required tension. The loads sustained at 0 and 120 degrees of knee flexion represented 50% and 36% of their maximum voluntary contraction (MVC) respectively. MVC was measured at 0 degree knee flexion. During the contractions, electromyograms (EMG) from the surface of the triceps surae muscles were recorded. Changes in the synergistic behaviour of the triceps surae were assessed via partial correlations of the average EMG (AEMG) between three muscle combinations; MG/LG, MG/SOL, LG/SOL, and correlation between SOL/MG + LG and MG/SOL + LG. The latter combinations were based on either common fibre type or innervation properties. Two types of synergisms were identified: trade-off and coactivation. Trade-off and coactivation synergies were defined by significant (p less than 0.05) positive and negative correlations respectively. Coactivation synergism was found to occur predominantly under conditions of high load or reduced length of the triceps surae, and increased with the duration of the contraction. Trade-off synergism was evident when the muscles were at their optimum length and the loads sustained were submaximum.(ABSTRACT TRUNCATED AT 250 WORDS)
Strength-velocity relations and fatigue resistance in an arm bench press manoeuvre were compared between conditions of bilateral (BL, both arms acting together) and unilateral muscle contraction in 9 young men. BL and UL (sum of the 2 arms acting singly) strength was similar for isometric and slow isokinetic maximal voluntary contractions (MVC); at high velocities BL MVC declined more than UL. In both types of contractions a curvilinear relation was observed between strength and velocity, with significantly higher peak torques (PT) being produced under isometric conditions than for slow velocity efforts (p less than 0.01). Mean declines in PT during 100 repetitive MVCs of approximately 70s were to 25% of initial values for the BL fatigue test and to 37% for UL (p less than 0.01). In contrast to results of a similar investigation of leg extension in the same subjects, the arms showed no BL deficit of strength in the initial part of the strength-velocity curve and approximately twice as much fatigue in repetitive contractions. These physiological differences may stem from the varying habitual activity patterns of the arms and legs.
The central changes associated with a period of strength training have been investigated in a group of 32 young healthy volunteers. Subjects participated in one of three 12 week training programmes, which required different degrees of skill and coordination. Study 1 consisted of unilateral isometric training of the quadriceps with the contralateral leg acting as a control, the apparatus providing firm back support and a lap strap. In Study 2 training consisted of unilateral concentric leg-extension with back support and hand-grips. In Study 3 subjects performed bilateral leg-extension with no back support. Measurements of maximum voluntary isometric strength were made at 2-3 week intervals and a continual record was kept of the weights lifted in Studies 2 and 3. The largest increase in isometric force was seen for the trained leg in Study 1 (approximately 40%). There was no significant change in strength in the contralateral untrained leg. In Studies 2 and 3 there was a large increase in training weights (about 200%) associated with smaller increase in isometric force (15-20%). It is concluded that a large part of the improvement in the ability to lift weights was due to an increased ability to coordinate other muscle groups involved in the movement such as those used to stabilise the body. The importance of these findings for athletic training and rehabilitation is discussed.
Article
Differences in electromyographic (EMG) activity between brief isometric maximum voluntary contractions under conditions of agonist contraction and agonist-antagonist co-contractions were assessed for elbow flexors (biceps brachii) and elbow extensors (triceps, long head). Expressing maximum EMG co-contraction activity as a ratio of agonist maximum EMG activity of the same muscle yielded EMG ratios consistently below 1.0 (mean = 0.48 for flexion and 0.76 for extension). Flexor EMG ratios did not co-vary with elbow position but extensor EMG ratios approached 1.0 or sometimes greater at shorter muscle lengths (elbow extension). Findings were in general accord with Sherrington's original proposal of 'double reciprocal innervation'. Neural circuitry designed to limit full muscle activation during co-contractions may serve to protect the joint against excessive tangential or compressive forces.
Article
Increases in leg power production resulting from 8 wk of bicycle endurance training (30 min/day, 5 times/wk) were studied using an isokinetic dynamometer. In addition, biopsies of vastus lateralis were analyzed to characterize muscle ultrastructural changes. Performance increased on the dynamometer specifically near the estimated average knee angular velocity used during the bicycle training (200 degrees/s). Power measurements were made during the first 5 contractions (maximal power: Pmax) and last 5 contractions (final power: Pend) of 25 and 50 consecutive contractions (at 60 and 240 degrees/s, respectively). Pmax and Pend increased only at 240 degrees/s but not at 60 degrees/s. These increases in Pmax (86 W) and Pend (78 W) resulted primarily from longer torque maintenance but also from increased peak torque during each contraction and were close to the increase in mechanical power output maintained on the bicycle (Pb; 78 W) during the training sessions. The specificity of these changes to the angular velocities used in the bicycle training indicates a neural basis to these adaptations. We suggest that these neural adaptations, coupled with the observed enhancement of muscle mitochondrial and capillary density (+41 and +15%, respectively) underlie the increased ability to maintain power production on a bicycle after endurance training.
Article
Experiments were designed to evaluate changes in the electrical activation and force generating capabilities of human soleus muscle during sustained, maximum isometric contractions. Eighteen experiments were conducted on 7 healthy subjects. Surface EMG, and in select cases, intramuscular fine wire EMG recordings, were made to assess the electrical activation of soleus. Subjects performed maximum isometric plantarflexion contractions of 1-3 min during which time supramaximal electrical pulses were delivered to the tibial nerve at 5-s intervals to elicit maximum M waves. M wave areas were assessed for evidence of neuromuscular junction failure. The results revealed that, on average, maximum force declined to 80% of unfatigued maximum by 60 s of effort, 74% by 90 and 120 s, and 70% by 180 s. M waves were stable for efforts up to 3 min, thereby providing little evidence for neuromuscular junction failure. In 3 experiments, total spike counts from intramuscular recordings displayed a 50% reduction in firing by 30 s of effort, with little additional slowing for up to 3 min. Although all of the fatigue-induced electrical and mechanical alterations in muscle activation reported earlier for intrinsic hand and foot muscles were verified in these experiments on soleus, the magnitudes and time courses of these changes were quite different. All changes were consistent with a muscle designed to optimally resist fatigue.
Article
Ten well-trained male volleyball players performed one-legged and two-legged vertical countermovement jumps. Ground reaction forces, cinematographic data, and electromyographic data were recorded. Jumping height in one-legged jumps was 58.5% of that reached in two-legged jumps. Mean net torques in hip and ankle joints were higher in one-legged jumps. Net power output in the ankle joint was extremely high in one-legged jumps. This high power output was explained by a higher level of activation in both heads of m. gastrocnemius in the one-legged jump. A higher level of activation was also found in m. vastus medialis. These differences between unilateral and bilateral performance of the complex movement jumping were shown to be in agreement with differences reported in literature based on isometric and isokinetic experiments.
Article
To investigate the influence of explosive type strength training on isometric force- and relaxation-time and on electromyographic and muscle fibre characteristics of human skeletal muscle, 10 male subjects went through progressive training which included primarily jumping exercises without extra load and with light extra weights three times a week for 24 weeks. Specific training-induced changes in force-time curve were observed and demonstrated by great (P less than 0.05-0.01) improvements in in parameters of fast force production and by a minor (P less than 0.05) increase in maximal force. The continuous increases in fast force production during the entire training were accompanied by and correlated with the increases (P less than 0.05) in average IEMG-time curve and with the increase (P less than 0.05) in the FT:ST muscle fibre area ratio. The percentage of FT fibres of the muscle correlated (P less than 0.05) with the improvement of average force-time curve during the training. The increase in maximal force was accompanied by significant (P less than 0.05) increases in maximum IEMGs of the trained muscles. However, the hypertrophic changes, as judged from the anthropometric and muscle fibre area data, were only slight during the training. It can be concluded that in training for fast force production considerable neural and selective muscular adaptations may occur to explain the improvement in performance, but that genetic factors may determine the ultimate potential of the trainability of this aspect of the neuromuscular performance.
Article
Eleven male subjects (20-32 years) accustomed to strength training went through progressive, high-load strength training for 24 weeks with intensities ranging variably between 70 and 120% during each month. This training was also followed by a 12-week detraining period. An increase of 26.8% (P less than 0.001) in maximal isometric strength took place during the training. The increase in strength correlated (P less than 0.05) with significant (P less than 0.05-0.01) increases in the neural activation (IEMG) of the leg extensor muscles during the most intensive training months. During the lower-intensity training, maximum IEMG decreased (P less than 0.05). Enlargements of muscle-fibre areas, especially of fast-twitch type (P less than 0.001), took place during the first 12 weeks of training. No hypertrophic changes were noted during the latter half of training. After initial improvements (P less than 0.05) no changes or even slight worsening were noted in selected force-time parameters during later strength training. During detraining a great (P less than 0.01) decrease in maximal strength was correlated (P less than 0.05) with the decrease (P less than 0.05) in the maximum IEMGs of the leg extensors. This period resulted also in decreases (P less than 0.05) of the mean muscle-fibre areas of both fibre types. It was concluded that improvement in strength may be accounted for by neural factors during the course of very intensive strength training. Selective training-induced hypertrophy also contributed to strength development but muscle hypertrophy may have some limitations during long-lasting strength training, especially in highly trained subjects.
MU potentials of m.rectus femoris were led off with the help of needle electrodes under isometric contraction (up to 50% of the maximal strength). As many as 10 MUs, could be identified simultaneously. The experiments showed that under conditions of a fixed posture and a stable movement task, the order of recruitment and switch-off of motoneurones was usually stable. "Group behaviour" was typical when the strength of contraction changed the frequencies of different motoneurones changing in one direction. Such a pattern of behaviour of motoneurones agrees with the ideas of diffuse distribution of excitation in a motoneurone pool and of the organization of its activity on the basis of the "size principle" described by Henneman and co-workers. However, occasional independent changes in frequency of individual motoneurones and sub-groups of motoneurones were observed even under stable conditions of muscle contraction. Independent behaviour of motoneurones was particularly frequent in the case of a subject in a free posture or when his movement task was changed. In such cases, the recruitment order of motoneurones was not stable, discharge frequencies quite often changing in opposite directions and substitution of motoneurones occurring. This pattern of motoneurone behaviour can be explained only by the use of independent inputs. The data obtained give us reason to believe that the organization of activity of a motoneurone pool on the basis of general diffuse input can provide only standard forms of motor activity. Under natural conditions of movement of higher animals and man, in addition to differences in thresholds another more flexible mechanism of selective activation of motoneurones is employed. This mechanism secures a more subtle regulation of mechanical effect and prevents fatigue during prolonged contraction of a muscle by causing substitution of MUs through changes in posture.
Article
The effects of seven weeks of eccentric or concentric muscle conditioning on muscle tension and. integrated electrical activity (IEMG) were investigated on human subjects by using a special electrical dynamometer as a testing and training apparatus. The eccentric conditioning caused, on the average, a greater improvement in muscle tension than did the concentric conditioning. In early conditioning those in the eccentric group experienced soreness in their exercised muscles. This caused a concomitant drop in maximum strength. After the disappearance of pain symptoms, ability to develop tension increased in a linear fashion. Neither method was able to cause statistically significant changes in the maximum IEMG associated with any type of muscle contraction. The regression lino expressing the relationship between IEMG ( μ.v. per sec.) and isometric tension (in percent of maximal voluntary contraction) was parabolic. In this relationship muscle conditioning failed to cause any significant changes in IEMG per unit of tension. Although the IEMG changes due to conditioning were somewhat different in the two experimental groups, it could not be established that either type of conditioning caused increase in the desynchronized firing of motor units.
Article
The discharge pattern and recruitment order of single motor units in voluntary contraction of the normal human anterior tibial muscle was studied with an electrode having a high selectivity and a high positional stability in the muscle. In sustained contractions each motor unit was activated at a characteristic level of tension. The higher the threshold of the motor unit in sustained contraction, the higher was the frequency when the unit attained a discharge at regular intervals and the higher tended the “maximum frequency‘-of the unit to be. Motor units with low thresholds in sustained contractions exhibited a continuous or tonic discharge in strong sustained contractions, whereas units with high thresholds tended to exhibit a discontinuous or phasic discharge. For some units the threshold of activation remained stable, for others it increased during activity. In twitch contractions the recruitment order of motor units differed considerably from that in sustained contractions.
Article
A study has been made of the effect of voluntary contraction on the `late' responses which can be recorded in muscles after indirect stimulation. Two late responses have been described of which the first was shown to consist mainly of a potentiated H-reflex. The potentiation of this wave was greatest in the abductor pollicis brevis muscle and depended largely on `direct' descending pathways to motoneurones. In addition, a later evoked muscle response appeared during effort; the nature of this wave was uncertain. Simple formulae have been devised to express the excitability of motoneurones to inputs from muscle nerves during effort.