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Neural Factors Versus Hypertrophy in the Time Course of Muscle Strength Gain
Abstract
The time course of strength gain with respect to the contributions of neural factors and hypertrophy was studied in seven young males and eight females during the course of an 8 week regimen of isotonic strength training. The results indicated that neural factors accounted for the larger proportion of the initial strength increment and thereafter both neural factors and hypertrophy took part in the further increase in strength, with hypertrophy becoming the dominant factor after the first 3 to 5 weeks. Our data regarding the untrained contralateral arm flexors provide further support for the concept of cross education. It was suggested that the nature of this cross education effect may entirely rest on the neural factors presumably acting at various levels of the nervous system which could result in increasing the maximal level of muscle activation.
... Despite a lack of significant improvement in the structural qualities of the VL and RF muscles, MVC peak torque still improved by greater than 22% for both sexes during the retraining program relative to post-immobilization, suggesting that the recovery of strength during retraining may have been mediated by neural factors. These retraining adaptions appear similar to those previously reported during the early phases of resistance training (Moritani and deVries 1979;Blazevich et al. 2007). ...
... Reduction in motor cortical size, reductions in voluntary activation, and alterations in motor unit recruitment and firing frequency behavior have been underlying mechanisms reported to explain why muscle strength loss outpaces atrophy (Liepert et al. 1995;Berg et al. 1997;Hortobágyi et al. 2000;MacLennan et al. 2021). Considering these alterations are quite plastic and that resistance training has been established as a potent stimulus for improving neuromuscular outcomes (Moritani and deVries 1979;Enoka 1988;Sale 1988;Carroll et al. 2001;Folland and Williams 2007), it was expected that relative strength would increase rapidly during the retraining program. In conjunction, the patterns of muscle atrophy and re-accrual between sexes likely contributed to the rapid increase in specific torque. ...
... Future research is needed to elucidate the specific neural mechanisms responsible for the recovery of strength in the absence of hypertrophy immediately following immobilization. Such findings may provide insight into whether these adaptations fully mimic those observed in the early phases of traditional resistance training (Moritani and deVries 1979;Blazevich et al. 2007), and may provide more insight into whether resistance training status may play an influential role in the recovery of strength following immobilization. Future studies are also needed to determine how the time course of strength recovery changes with increased immobilization duration. ...
This manuscript represents the second phase of a clinical trial designed to examine the effects of knee joint immobilization and retraining on muscle strength and mass. In Phase 2, we examined sex differences in the recovery of multiple indices of muscle quality after a resistance training-based rehabilitation program. Following 1 week of immobilization, 27 participants (16 males, 11 females) exhibiting weakness underwent twice weekly resistance training sessions designed to re-strengthen their left knee. Unilateral retraining sessions utilizing leg press, extension, and curl exercises were conducted until participants could reproduce their pre-immobilization knee extension isometric maximal voluntary contraction (MVC) peak torque. Post-immobilization, both sexes demonstrated impaired MVC peak torque (males = −10.8%, females = −15.2%), specific torque (−9.8% vs. −13.1%), echo intensity of the vastus lateralis (+6.9% vs. +5.9%) and rectus femoris (+5.9% vs. +2.1), and extracellular water/intracellular water ratio (+7.8% vs. +9.0%). The number of retraining sessions for peak torque to return to baseline for males (median = 1, mean = 2.13) versus females (median = 2, mean = 2.91) was not significantly different, though the disparity in recovery times may be clinically relevant. Following retraining, specific torque was the only muscle-quality indicator that improved along with MVC peak torque (males = 20.1%, females = 22.4%). Our findings indicate that measures of muscle quality demonstrate divergent recovery rates following immobilization, with muscle mass lagging behind improvements in strength. Greater immobilization-induced strength loss among females suggests that sex-specific rehabilitation efforts may be justified.
... Muscular strength improvements in response to strength training result from both neural and muscular adaptations (Moritani & deVries, 1979;Narici et al., 1989). Although these responses are likely triggered simultaneously at the commencement of a strength training programme, neural adaptations such as improvements in motor unit recruitment and rate coding are considered to predominate during the initial stages of strength gain (Del Vecchio et al., 2019), while hypertrophic adaptations are likely to be more important after several weeks of training in previously untrained muscles (Moritani & deVries, 1979;Narici et al., 1996). ...
... Muscular strength improvements in response to strength training result from both neural and muscular adaptations (Moritani & deVries, 1979;Narici et al., 1989). Although these responses are likely triggered simultaneously at the commencement of a strength training programme, neural adaptations such as improvements in motor unit recruitment and rate coding are considered to predominate during the initial stages of strength gain (Del Vecchio et al., 2019), while hypertrophic adaptations are likely to be more important after several weeks of training in previously untrained muscles (Moritani & deVries, 1979;Narici et al., 1996). While these responses are traditionally considered to occur in untrained individuals, muscles that have already encountered loading and thus have already undergone hypertrophy and increased activation might have less reserve for change (Häkkinen et al., 1987). ...
... If so, asymmetric training responses may be more likely in upper-body muscles than lower-body muscles. Interestingly, Moritani and deVries (1979) observed that hypertrophy predominantly contributed to strength changes later in the weaker (6 weeks) than stronger (two weeks) elbow flexors following isoinertial strength training, possibly indicating that strength increases in the weaker arm were associated with neural adaptations for a longer period of the training. Recently, Carvalho and Barroso (2020) reported that baseline 1-RM strength and muscle thickness were the same between the elbow flexors, and that they adapted similarly to the same relative isoinertial training stimulus. ...
Purpose. The present study quantified between-limb responses to strength training in the stronger (STR) versus weaker (WEA) elbow flexors in participants with symmetric (SYM) or asymmetric (ASY) 1-RM strength. Methods. Neural, hypertrophic and strength adaptations to 4 weeks (3∙wk-1) of unilateral elbow flexion training of both arms were examined in 24 participants (6 men and 6 women in each group) who had not undertaken strength training in the past 12 months. Changes in one-repetition maximum load (1-RM strength), isokinetic (20°·s-1 and 210°·s-1) and isometric (MVIC) strength and rate of force development (RFD) as well as muscle activation (EMG; normalised to maximum M-wave amplitude) and size (CSAFlexor) were measured. Transcranial magnetic stimulation was used to assess motor evoked potential amplitude (MEP) and cortical silent period duration (cSP). Results. Following training, significant increases in 1-RM strength (SYM, STR: ∆ = 2.4±1.1 kg, WEA: ∆ = 1.9±1.1 kg; ASY, STR: ∆ = 1.8±0.7 kg, WEA: ∆ = 1.7±0.7 kg) and CSAFlexor (SYM, STR: ∆ = 107±98 mm2, WEA: ∆ = 121±64 mm2; ASY, STR: ∆ = 108±73 mm2, WEA: ∆ = 105±65 mm2) were observed, although they were not different between arms in either group. Increases in isokinetic strength were also detected, but only in STR (SYM: 20°·s-1, 210°·s-1; ASY: 20°·s-1). No statistical changes were detected in MVIC, RFD, EMG, MEP or cSP. Correlation analyses demonstrated both similarities and differences in the between-limb responses when comparing the groups. Conclusion. Between-limb responses to strength training in participants with and without strength symmetry were similar, although isokinetic strength increases were only observed in the stronger arms. However, the correlation results suggest that individual differences exist between the groups, signalling that between-limb responses can differ in individuals with and without strength asymmetry.
... A common observation in short-term resistance training (<4 weeks) has been an increase in maximal voluntary contraction force (MVC) far exceeding muscle hypertrophy 1) . Neural adaptations such as increased agonist muscle activity have been considered as the major physiological mechanisms of this phenomenon 2,3) . The adaptation occurs in an early stage from onset of resistance training 4) . ...
... Many earlier studies have demonstrated that MVC is proportional to muscle cross-sectional area 6) . Considering that short-term resistance training increases MVC without muscle hypertrophy 4) , MVC per muscle cross-sectional area (MVC/mCSA), called specific tension 7) , is increased by resistance training 1,3) . Erskine et al. 8) have demonstrated that the individual variability of increase in MVC depends on the specific tension for a 9-week resistance training. ...
... In this study, the 3-week isometric training to volitional failure increased MVC and MVC/mCSA. The increase in MVC by resistance training occurs in the early stage (<4 weeks) 4) , and depends on neural adaptations such as increased agonist muscle activity 2,3,16) . As another mechanism of early strength gain due to isometric training, muscle contractile properties could change due to isometric training. ...
We tested a hypothesis that individuals with low maximal voluntary isometric contraction relative to muscle cross-sectional area (MVC/mCSA) would have greater strength gain compared to those with high MVC/mCSA in an early stage from beginning of isometric training to volitional failure. Male adults (n = 24; 22.4 ± 2.5 years, 174.1 ± 6.5 cm, 75.8 ± 14.1 kg) conducted a 3-week isometric training to volitional failure (60-80% MVC, 2-3 times/week, 3 sets/session) in elbow joint flexion with 90° flexion of each arm. Based on the relationship between MVC and mCSA before the intervention, we assigned 16 arms to the higher group (HIGH), 14 to the lower group (LOW) and 18 to the mean group (MEAN). Before the intervention and at the beginning of every week, we measured MVC (myometer) and muscle thickness of anterior upper arm (ultrasound). The mCSA was derived from muscle thickness. The 3-week isometric training to volitional failure increased MVC in all groups, but the relative change in MVC through the intervention was higher in LOW than in HIGH and MEAN groups. The current findings of this study support the abovementioned hypothesis.
... Muscle growth and strength gains are well known adaptations to resistance training and these two variables are classically linked in that it is thought that muscle growth drives changes in strength (1,2). Identifying factors that can influence exercise induced muscle growth may be important for maximizing long term changes in strength. ...
... This suggests that the change in strength observed were likely explained by mechanisms other than changes in muscle size. Changes within the nervous system are theorized to play a role in strength changes(2). It is possible that such changes may have played a role in the current study. ...
Changes in skeletal muscle size may be affected by resting blood flow (e.g., nutrient delivery) and this change in size is a hypothesized mechanism for changes in strength.
Purpose
To determine: 1) whether the relationship between isometric training and muscle growth depends on baseline blood flow or is mediated by a change in blood flow and 2) whether muscle growth mediates changes in maximal isometric strength.
Methods
179 participants were randomized into: low-intensity isometric handgrip exercise (LI), low-intensity isometric handgrip exercise with blood flow restriction (LI-BFR), maximal handgrip exercise (MAX), and a non-exercise control (CONTROL). Muscle thickness, strength, and resting limb blood flow were measured before and after the six-week intervention.
Results
Baseline blood flow did not moderate training effects on muscle thickness changes (MTHchg) ( p = 0.666), and moderated mediation tests were non-significant. Although the LI-BFR group showed a significant effect on MTHchg ( p = 0.018), MTHchg was not significantly related to handgrip strength change (HGchg) ( p = 0.281), suggesting no mediation of the training-to-strength effect by MTHchg. Both the LI-BFR ( p = 0.004) and MAX ( p < 0.001) groups exhibited positive direct effects on HGchg compared to CONTROL. Furthermore, there were no differences between training groups and CONTROL on blood flow change (BFchg), BFchg and MTHchg were not significantly related, and neither BFchg nor MTHchg predicted HGchg, providing no evidence for mediated pathways.
Conclusions
Muscle growth may not have occurred to an extent that would require vascular adaptation. Training maximally induced the greatest strength adaptations but was seemingly not driven by muscle growth.
... However, interestingly, SPANOVA analysis showed that the interaction effect was not statistically significant (Wilk's lambda = 0.338), indicating there was no difference in body composition for the three groups pre-and post-intervention. Our results were in agreement with that of Slentz and colleagues' (21), who also reported that physical activity is associated with significant reductions in body weight and fat mass in overweight and obese middle aged men and women in a dose-response manner. ...
... The study's twelve week duration indicates that the increases in muscular strength for this study are not just due to neural adaptations or to increased motor unit recruitment. The study's twelve week duration demonstrated that, collectively, the learned recruitment of additional motor units, the increased activation of synergistic muscles, and the inhibition of neural protective mechanisms (21), all contributed to enhance the muscle's ability to generate more force, thus the improvement of strength in the push up, curl up, and bodyweight squat results post intervention. = 0.289). ...
... It has been observed that the contralateral increases in muscle strength Communicated by William J. Kraemer. are not usually accompanied with an increase in muscle size (Moritani and deVries 1979;Hortobágyi et al. 1996;Dankel et al. 2020), and are therefore most likely driven by neural adaptations (Moritani and deVries 1979;Farthing et al. 2005;Carroll et al. 2006;Ruddy et al. 2017). In addition, the available evidence would suggest that exercise with higher loads (> 70% one-repetition max [1RM]) induces a greater cross-education response than lower load (30% 1RM) exercise (Colomer-Poveda et al. 2021;Pelet and Orsatti 2021;Bell et al. 2023). ...
... It has been observed that the contralateral increases in muscle strength Communicated by William J. Kraemer. are not usually accompanied with an increase in muscle size (Moritani and deVries 1979;Hortobágyi et al. 1996;Dankel et al. 2020), and are therefore most likely driven by neural adaptations (Moritani and deVries 1979;Farthing et al. 2005;Carroll et al. 2006;Ruddy et al. 2017). In addition, the available evidence would suggest that exercise with higher loads (> 70% one-repetition max [1RM]) induces a greater cross-education response than lower load (30% 1RM) exercise (Colomer-Poveda et al. 2021;Pelet and Orsatti 2021;Bell et al. 2023). ...
Introduction
The application of blood flow restriction (BFR) to low-intensity exercise may be able to increase strength not only in the trained limb but also in the homologous untrained limb. Whether this effect is repeatable and how that change compares to that observed with higher intensity exercise is unknown.
Purpose
Examine whether low-intensity training with BFR enhances the cross-education of strength compared to exercise without BFR and maximal efforts.
Methods
A total of 179 participants completed the 6-week study, with 135 individuals performing isometric handgrip training over 18 sessions. Participants were randomly assigned to one of four groups: 1) low-intensity (4 × 2 min of 30% MVC; LI, n = 47), 2) low-intensity with blood flow restriction (LI + 50% arterial occlusion pressure; LI-BFR, n = 41), 3) maximal effort (4 × 5 s of 100% MVC; MAX, n = 47), and 4) non-exercise control (CON, n = 44).
Results
LI-BFR was the only group that observed a cross-education in strength (CON: 0.64 SD 2.9 kg, LI: 0.95 SD 3.6 kg, BFR-LI: 2.7 SD 3.3 kg, MAX: 0.80 SD 3.1 kg). In the trained hand, MAX observed the greatest change in strength (4.8 SD 3.3 kg) followed by LI-BFR (2.8 SD 4.0 kg). LI was not different from CON. Muscle thickness did not change in the untrained arm, but ulna muscle thickness was increased within the trained arm of the LI-BFR group (0.06 SD 0.11 cm).
Conclusion
Incorporating BFR into low-intensity isometric training led to a cross-education effect on strength that was greater than all other groups (including high-intensity training).
... Regular participation in resistance-training increases maximal strength and force production. It is generally accepted that upon initiating a novel resistance-training program, neural adaptations facilitate the initial, rapid increase in maximal force production, whereas skeletal muscle hypertrophy becomes more prominent after several weeks of training [1,2]. The rapid improvement in maximal force following only a few weeks of training has led some to suggest that there is a large motor skill component to resistance-training [3,4]. ...
... A second, alternative explanation is that chronic exposure to resistancetraining may exert a ceiling effect for neural adaptations, such that the performance of motor imagery may not increase corticospinal excitability to a greater extent than that observed in untrained participants. This theory is consistent with the time course of specific adaptations, with the early phases of resistance-training being largely controlled by neural adaptations [1,10]. A third and perhaps most relevant explanation is that the imagined task and assessment of corticospinal excitability for the FDI did not adequately reflect the training experience of the participants. ...
Both motor imagery and resistance–training enhance motor function and corticospinal excitability. We tested the hypothesis that young participants with significant resistance–training experience would show heightened corticospinal excitability during a single session of motor imagery training. Fifty-six participants (mean ± SD age = 22 ± 2 years) were divided into resistance–trained and untrained groups. Forty-one upper-body resistance trained (21 males, 20 females; mean ± SD relative one repetition maximum bench press = 0.922 ± 0.317 kg/kg) and 15 untrained (4 males, 11 females; mean ± SD relative one repetition maximum bench press = 0.566 ± 0.175 kg/kg) participants visited the laboratory on three separate occasions. The first visit served as the familiarization session. During visits 2 and 3, participants engaged in a hand/wrist motor imagery protocol or rested quietly (control condition) in a randomized order. Before and after the interventions, single-pulse transcranial magnetic stimulation (TMS) over the motor cortex was used to measure resting motor–evoked potential amplitude of the first dorsal interosseous muscle. Our main finding was that motor imagery acutely increased corticospinal excitability by ~64% (marginal means pre = 784.1 µV, post = 1246.6 µV; p < 0.001, d = 0.487). However, there was no evidence that the increase in corticospinal excitability was influenced by resistance–training experience. We suspect that our results may have been influenced by the specific nature of the motor imagery task. Our findings have important implications for motor imagery prescription and suggest that motor imagery training may be equally beneficial for both resistance–trained and untrained populations. This study was prospectively registered at ClinicalTrials.gov (Identifier: NCT03889548).
... This is especially true if measured in the task that was specifically trained (Martin-Hernandez et al., 2013;. The reason for this change in strength is not known but classic exercise physiology would suggest that early changes are due to neural adaptations followed by large contributions from muscle hypertrophy (Ikai & Fukunaga, 1970;Moritani & deVries, 1979). Popular as it may be, the experimental support for that idea is lacking and more recent work has failed to find an advantage of muscle growth for changes in muscle strength (Buckner et al., 2021;Mattocks et al., 2017). ...
... During familiarization, an increase in descending neural drive facilitates this early adaptation by enhancing the activation of trained muscle [32][33][34][35][36][37][38] . This finding aligns with Moritani and deVries, who found that neural changes account for rapid increases in strength at the onset of strength training for untrained individuals 39 . Another study suggests that the increased force production observed from familiarization to baseline is attributed to a reduced motor unit recruitment threshold and enhanced central activation, driven by the high initial levels of central activation achieved during the familiarization session 21 . ...
This study examined the number of contractions required for an isometric plantar flexion familiarization. Twenty-six males were separated into two independent Groups: Group A: where five contractions were initiated on the dominant limb (right) followed by the contralateral limb; and Group B, initiated by the non-dominant limb (left) followed by the dominant limb. Participants carried out a 5-s maximum voluntary contraction (MVC), with an interpolated twitch administered to the tibial nerve. In Group A, both the dominant and non-dominant limbs required two contractions for familiarization, whereas in Group B, the dominant limb required two contractions, and the non-dominant limb required three (p < 0.05). A strong relationship between MVC and voluntary activation (VA) was observed in Group A for the D (r = 0.91, p < 0.05) and in Group B for the ND limb (r = 0.99, p < 0.05). The results demonstrated evidence of cross-limb transfer from the dominant to the non-dominant limb (p < 0.05). This phenomenon implicates central involvement, substantiated by VA responses that mirror the changes in MVC. Practitioners and researchers should consider the impact of cross-limb transfer during a single familiarization session when assessing strength to avoid overestimation of the gains. Future cross-education/cross-limb transfer studies could investigate the central mechanisms involved during familiarization.
... Watanabe et al. (2021) previously reported that short-term isometric exercise training (three sets of 10 contractions at 80%MVC) can improve muscle strength in young and older individuals (Watanabe et al., 2020). Furthermore, it has been well-established that short-term resistance exercise training can induce neural adaptations (Sale, 1988), resulting in an increases in muscle strength even in the absence of increases in muscle size (Akima et al., 1999;Moritani & deVries, 1979;Pearcey et al., 2021). Although Balshaw et al. (2017) reported that pre-training muscle strength also contributed to muscle strength gains after resistance exercise training, PRE training muscle strength did not differ between groups (Figure 2). ...
This study investigated whether home‐based bathing intervention (HBBI) improve muscle strength gain and protect cardiovascular function by short‐term resistance training (RT). Thirty‐one healthy young men measured the maximum voluntary isometric contraction (MVC) of knee extensor, electrically evoked knee extension torque, and mean arterial pressure (MAP). Then, participants were divided into three groups with matching MVC: shower without bathing (control, n = 10), thermoneutral bathing (36°C‐bathing, n = 10), and hot bathing (40°C‐bathing, n = 11), and conducted 2 weeks of HBBI. Following familiarization for HBBI, participants completed 2 weeks of HBBI and acute RT (five sessions of three sets of 10 isometric knee extension at 60% MVC). Baseline neuromuscular and cardiovascular function was assessed again following completion of the 2 weeks of intervention. MVC was non‐significantly increased after the RT period in 40°C‐bathing with large effect size (partial η² = 0.450). The electrically evoked knee extension torque (10/100‐Hz ratio) was significantly increased after the RT period in control (p = 0.020). MAP did not alter due to bathing intervention and RT (all p > 0.05). HBBI improved muscle strength without RT‐induced alteration of peripheral muscle condition. Shower without bathing reduced muscle strength gain but increased peripheral muscle condition. Short‐term RT does not adversely affect the cardiovascular function, regardless of HBBI.
... As a novel, low-velocity resistance exercise modality, variations of EQI resistance exercise (EQI-RE) are proposed to acutely increase motor unit recruitment, muscle co-contraction/activation, and time under tension, potentially to a greater degree than traditional isotonic resistance exercise (Morrison, 2016;Oranchuk et al., 2019b;Seedman, n.d.-a, n.d.-b;Sinicki, 2019). Since time under tension and motor unit recruitment are implicated in strength and hypertrophy processes (Lim et al., 2022;Moritani & DeVries, 1979;Nuzzo, 2022;Pearson & Hussain, 2015;Schoenfeld, 2010;Zabaleta-Korta et al., 2020), it has been suggested that the EQI concept could lead to unique musculotendinous morphological and strength adaptations with chronic training (Morrison, 2016;Oranchuk et al., 2019b;Seedman, n.d.-a, n.d.-b;Sinicki, 2019). Despite these suggestions, few studies have investigated EQI-RE acutely or chronically, or compared it to other forms of resistance exercise. ...
Traditional isotonic resistance exercise (TRD-RE) improves muscle mass, strength, and overall health. However, TRD-RE may be impractical or unfeasible in injury or sport specific situations. Compared to TRD-RE, eccentric quasi-isometric resistance exercise (EQI-RE) is a low-velocity resistance exercise modality suggested to acutely produce similar and/or greater time under tension, motor unit recruitment, and antagonist co-activation. With limited investigations or comparisons to other forms of resistance exercise, however, evidence is lacking. As differences between males and females exist in time under tension and motor unit behaviour in other resistance exercise contexts, the current study explored sex-differences in time under tension and surface electromyography (sEMG) across 2 sets of TRD-RE and EQI-RE. Twenty-seven (n = 13 females) participants performed unilateral TRD-RE and EQI-RE of the elbow flexors while sEMG was collected from the biceps and triceps brachii. Several main and interaction effects of resistance exercise type, set, and sex were present for time under tension, linear envelope peak (LEpeak), absolute (iEMGabs) and relative (iEMG%) integrated sEMG, with set 1 typically having higher sEMG values than set 2, and EQI-RE having greater time under tension than TRD-RE. Notably, females produced significantly more time under tension, iEMGabs, iEMG%, and co-activation than males during EQI-RE, while males experienced a more significant set-to-set reduction in time under tension and LEpeak during TRD-RE. Overall, TRD-RE may result in quicker voluntary excitation and subsequent fatigue of motor units compared to EQI-RE, while females may accrue more resistance exercise volume than males when performing EQI-RE. Theoretically, these effects could lead to long-term sex-differences in strength and hypertrophy outcomes between males and females, TRD-RE and EQI-RE.
... Initial gains are typically evident after 4 weeks of resistance training (Del Vecchio et al., 2019a;Lecce et al., 2024b) and primarily attributed to neural modifications (Sale, 1988;Del Vecchio et al., 2024), including motor unit adaptations either independently or in conjunction with morphological changes (Duchateau et al., 2006;Ansdell et al., 2020;Škarabot et al., 2021;Roberts et al., 2023). A typical instance of such early neural changes is cross-education, also known as cross-transfer or interlimb transfer (Manca et al., 2018), in which unilateral resistance training induces gain transfers to the contralateral untrained limb (Moritani and deVries, 1979;Manca et al., 2021;Kay et al., 2024). These gains seem specific to strength and skill transfer, as muscle endurance does not seem to transfer to the untrained side (Song et al., 2024). ...
Introduction
Early increases in muscle strength following unilateral resistance training are typically accompanied by strength gains in the contralateral untrained muscles, a phenomenon known as cross-education. However, the specific motor unit adaptations responsible for this gain transfer remain poorly understood. To address this gap, we recorded myoelectrical activity from the biceps brachii using high-density electromyography.
Methods
Nine participants performed 8-week unilateral resistance training and were compared to nine control individuals who did no intervention. Discharge characteristics of longitudinally tracked motor units were assessed during maximal voluntary contractions and isometric ramp contractions at 35% and 70% of the maximal voluntary force (MVF) at baseline (T0), 4 weeks (T1), and 8 weeks (T2) post-intervention.
Results
MVF increased by 7% in untrained muscles at T1 and 10% at T2 (p < 0.05). These gains were accompanied by significant decreases in motor unit recruitment thresholds (p < 0.01) and higher net discharge rate (i.e., gain in discharge rate from recruitment to peak) following intervention (p < 0.05). Trained muscles presented greater MVF (+11%, T1; +19%, T2) with similar motor unit adaptations, including a lower recruitment threshold (p < 0.01) and a higher net discharge rate (p < 0.01).
Discussion
Our findings indicate that higher strength in untrained muscles is associated with a higher net discharge rate, implying a greater spinal motoneuron output to muscles. The present results underscore the role of motor unit adaptations in the transfer of strength gains to non-trained muscles, offering novel insights into the neural mechanisms underlying cross-education.
... It is well known that both peripheral and neural adaptations modify muscle strength in healthy people. 20 Previous studies hypothesized that disruption of sensory input due to the pain, inflammation, and loss of mechanoreceptors following ACL rupture would alter the motor output of the muscles and lead to persistent disuse and atrophy of muscles and maladaptive neuroplasticity of CNS. The CNS controls muscle contractions via spinal reflexes and supraspinal adjustment through the CST, plays multiple roles in sensory and motor performance, and is related to quadriceps strength 7,13,14,21,23 ACLR disrupts sensory input from the quadriceps, which results in reduced sensitivity to electrochemical neuronal signals, an increase in central inhibition of neurons regulating quadriceps control. ...
Background: Persistent maladaptive changes of corticospinal tract (CST) and quadriceps strength deficits exist in
patients with anterior cruciate ligament reconstruction (ACLR). This study aimed to investigate the relationships
between the structural alterations of CST and quadriceps muscle strength deficits in patients with ACLR.
Methods: Twenty-nine participants who had undergone unilateral ACLR (29 males; age = 32.61 ± 6.72 years)
were enrolled in a cross-sectional investigation. We chose CST as a region of interest and performed diffusion
tensor imaging (DTI) that measured the microstructure of white matter tracts. Maximal voluntary isometric
quadriceps muscle strength was assessed using a hand-held dynamometer. Simple and partial correlation ana�lyses were performed between the DTI outcomes and quadriceps muscle strength deficits in patients with ACLR
before and after controlling for age, sex, BMI, Tegner activity score, and graft type. Sub-group analyses were also
performed to investigate the relationships between the DTI outcomes of CST structure and quadriceps muscle
strength deficits according to the graft type before and after controlling for age, sex, BMI, and Tegner activity
score.
Results: Lower limb symmetry index (LSI) of quadriceps muscle strength was associated with a higher ratio of
radial diffusivity (RD, r = − 0.379, p = 0.042) in corticospinal tracts of the injured hemisphere to those of the
non-injured hemisphere in ACLR patients after controlling for age, BMI, Tegner activity score and graft type. In
subgroup analyses of ACLR patients with hamstring autografts, we found that higher injured quadriceps muscle
strength was associated with higher axial diffusivity (AD, r = 0.616, p = 0.033) of CST structure and lower LSI of
quadriceps muscle strength was associated with higher ratio of mean diffusivity (MD, r = − 0.682, p = 0.014) and
RD (r = − 0.759, p = 0.004) in corticospinal tracts of the injured hemisphere to those of the non-injured
hemisphere in ACLR patients after controlling for age, BMI, Tegner activity score.
Conclusion: Decreased integrity (higher ratio of RD) of CST microstructure in ACLR patients was significantly
associated with lower quadriceps limb symmetry index, which hinted that quadriceps muscle strength deficits of
injured side may be a demyelinating process of CST microstructure in ACLR.
... The timeline for serial sarcomerogenesis appears to align with the overall temporal pattern of muscle hypertrophy, where increases in cross-sectional area become more prominent after 3 wk of training. 54,55 The present study provides evidence for the addition of sarcomeres in series as a longer-term adaptation to eccentric training. This suggests that with longer muscle fascicles due to serial sarcomere addition, at a given level of force, each sarcomere would be stretched less. ...
... Resistance training can be incorporated with manual, elastic, or dumbbells based on the preference of the clinician. Remember that neurophysiological adaptation during the first 3 weeks of resistance training while true hypertrophy takes several more weeks to be observed (Moritani and DeVries 1979). An integrated and simple way to strengthen multiple segments is to use a kinetic chain approach in which the athlete is standing in their functional position and add external resistance through their legs or arms while replicating diagonal motions of chopping and lifting as described by McMullen and Uhl (2000). ...
... It has also been established that neurological adaptations are the primary cause for improvements in strength within the first 3-4 weeks of resistance training (3, International Journal of Exercise Science http://www.intjexersci.com 127 4,11,13). Muscle hypertrophy, the increase in the size and function of a muscle fiber, is commonly seen in weeks 8-12 from the start of the training program (9,16,17). ...
Manipulating variables in a training program (e.g., sets, reps, lifts, sequence, etc.) is designed to maximize strength and power performance. Due to the complexity of designing resistance-training programs, changing one variable could potentially set an athletic team apart from others in performance. The purpose of this study was to investigate if exercise sequence could influence the development of strength, speed, and agility. This study compared two specific types of exercise sequences: traditional, which performs the prescribed exercises in a traditional or blocked manner (by completing every set of an exercise before moving to the next); and, circuit, which performs the prescribed exercises in a circuit or alternating manner (by completing the first set of each prescribed exercise, then going to the second set of each exercise). Thirty-nine adolescent athletes from two separate high school football teams completed identical six-week resistance-training programs with the only difference being the sequence of the exercises. Each group tested pre- and post-intervention on hang clean, bench, squat, 40-yard dash, and pro agility. A strength index was used to measure overall strength gained by dividing the sum of the three lifts by total body weight. The results demonstrated that the only significant difference between groups occurred with hang clean. Both circuit and traditional groups made significant but equal gains when compared independently pre- to post-intervention. These results suggest that if strength gains are desired, then either a circuit or traditional style of exercise sequence will produce equal results regardless of beginning level of strength.
... These improvements are consistent with those in our study and can be accounted for by increased neuromuscular activity (Hough, Ross & Howatson, 2009), PAP (Maloney, Turner & Fletcher, 2014), and increased temperature (Bishop, 2003b;Fletcher, 2010;Yamaguchi & Ishii, 2005). After the application of isometric contractions, strength gains associated with neural factors have also been verified (Moritani & DeVries, 1979;Kitai & Sale, 1989;Sale, 1988), as a consequence of PAP induction (Sale, 2004). This is consistent with our results after the application of VICAMS, and is justified by the theory that strength levels are optimized through increased contractile performance of the muscle when MVIF are included (Bishop, 2003a). ...
Background
Isometric training is used in sport, conventional physical activity and rehabilitation. Understandably, there is a great deal of research related to its effect on performance. It is known that the length of the muscle at the moment of contraction is a determinant of strength levels. In the literature we find research on isometric training in short muscle lengths, although it has not been studied in maximally shortened positions or the acute effects that occur after its application. Ballistic stretching (BS) is also popular in sport. Their execution involves actively reaching maximally shortened muscle positions. So far, isometric training has not been compared with protocols involving ballistic stretching. Considering the above, the aim of the present study was to investigate the effects of BS and voluntary isometric contraction at maximal shortening (VICAMS) on range of motion, strength and vertical jump.
Methods
The study involved 60 healthy, physically active individuals (40 and 52 years old) who were randomly assigned to three groups: BS, VICAMS and a control group (CG). To assess acute effects, before and after the intervention, active range of motion (AROM), maximal voluntary isometric force (MVIF) and countermovement jump height (CMJ) were determined.
Results
Time main effects and time*group interactions were found for all variables ( p < 0.001). Between-group differences were shown for the VICAMS group after the intervention, with statistically significant higher AROM values compared to the other groups. MVIF values were also higher in the VICAMS group. Intra-group differences were observed for the VICAMS and Ballistic groups, as values on all variables increased from baseline. For the CMJ, intra-group differences showed that both the VICAMS and BS groups improved values compared to baseline values.
Conclusions
The application of VICAMS induced acute improvements over BS in AROM, MVIF and CMJ. These results are important for coaches seeking immediate performance improvement and offer an optimal solution to the warm-up protocol.
... Geralmente, o treinamento para desenvolver a potência anaeróbia é fundamentado na necessidade de melhorar os sistemas ATP-CP e glicolítico. Para isso, a recomendação para o desenvolvimento da potência anaeróbia alática é de realizar exercícios intermitentes com duração entre 5 -25 s, recuperação entre 1,5 -Por outro lado, a hipertrofia muscular parece ocorrer mais tardiamente após algumas semanas de treinamento (MORITANI & DEVRIES, 1978). Embora exista uma tendência em associar aumento de força muscular como consequência de aumento da secção transversa do músculo, essa relação parece ser verdadeira apenas após o período de adaptações neurais (CHILLIBECK et al., 1998). ...
As lutas de jiu-jítsu demandam grande influência de força, velocidade, potência,
resistência anaeróbia e flexibilidade. De acordo com o IBGE, apenas 28,2 % da
população pratica algum tipo de exercício físico ou esporte. O principal motivo para
isso é a falta de motivação para as atividades. Como alternativa, encontramos
atividades fora do paradigma de exercícios criado pela sociedade. Sendo assim, o
presente estudo teve como objetivo avaliar algumas das capacidades físicas
determinantes para a prática do jiu-jítsu e essenciais para a saúde de um praticante,
bem como determinar a intensidade e características bioenergéticas dos combates.
Foram avaliados 16 voluntários não praticantes de jiu-jítsu, antes e após 12 sessões
de treinamento, realizados 2 vezes por semana, 1 hora por dia, durante 6 semanas.
Foram coletados dados de massa, composição corporal, estatura, capacidade
aeróbia, potência anaeróbia, força máxima dinâmica, teste de preensão manual e
flexibilidade. Os dados foram analisados através do teste T para amostras pareadas.
Não foram observadas alterações para massa, estatura e composição corporal. A
intensidade dos combates foi caracterizada através da frequência cardíaca (FC) e do
consumo de O2 como vigorosa. Pelo quociente respiratório (QR) e o limiar
ventilatório 2 (LV2), os combates demonstraram-se predominantemente anaeróbios.
Foram observados aumentos significativos para o VO2máx dos homens (H) e das
mulheres (M), tempo para exaustão (H e M) e FCmáx (H), na potência anaeróbia
máxima (H e M), e na potência anaeróbia média (H), na força máxima dinâmica em
ambos os grupos no agachamento, na força de preensão manual para a mão não
dominante para as mulheres e na flexibilidade para H. O delta foi calculado para
comparação do ganho entre grupos, o qual revelou maior ganho no grupo H apenas
para a capacidade flexibilidade. É possível concluir que um treinamento de jiu-jítsu,
promove aumento na capacidade aeróbia, potência anaeróbia, força muscular e
flexibilidade de seus praticantes.
... total sleep deprivation (Lamon et al, 2021) reduces muscle fractional synthesis rate. Muscle strength is dictated by a complex interaction of: number of parallel contractile elements, tissue quality and composition, contractile function, and motor unit recruitment (Chou et al. 2008; Moritani and deVries 1979). Although chronically insufficient sleep may reduce myofiber size (Saner et al. 2020;Lamon et al. 2021) this is unlikely to explain acute changes in strength following a single night of total sleep deprivation or a few consecutive nights of insufficient sleep. ...
Acute sleep restriction (SR) reduces strength through an unknown mechanism. Purpose: To determine how SR affects quadriceps contractile function and recruitment. Methods: Eighteen healthy subjects (9 M, 9F, age 23.8 ± 2.8y) underwent isometric (maximal and submaximal), isokinetic (300–60°·s⁻¹), and interpolated twitch (ITT) assessment of knee extensors following 3d of adequate sleep (SA; 7–9 h·night⁻¹), 3d of SR (5 h·night⁻¹), and 7d of washout (WO; 7-9 h·night⁻¹). Results: Compared to SA (227.9 ± 76.6Nm) and WO (228.19 ± 62.9Nm), MVIC was lesser following SR (209.9 ± 73.9Nm; p = 0.006) and this effect was greater for males (− 9.8 v. − 4.8%). There was no significant effect of sleep or sleep x speed interaction on peak isokinetic torque. Peak twitch torque was greater in the potentiated state, but no significant effect of sleep was noted. Males displayed greater potentiation of peak twitch torque (12 v. 7.5%) and rate of torque development (16.7 v. 8.2%) than females but this was not affected by sleep condition. ITT-assessed voluntary activation did not vary among sleep conditions (SA: 81.8 ± 13.1% v. SR: 84.4 ± 12.6% v. WO 84.9 ± 12.6%; p = 0.093). SR induced a leftward shift in Torque-EMG relationship at high torque output in both sexes. Compared to SA, females displayed greater y-intercept and lesser slope with SR and WO and males displayed lesser y-intercept and greater slope with SR and WO. Conclusions: Three nights of SR decreases voluntary isometric knee extensor strength, but not twitch contractile properties. Sex-specific differences in neuromuscular efficiency may explain the greater MVIC reduction in males following SR.
... A common repetition range for achieving muscle hypertrophy is six to twelve repetitions with a rest period of thirty to ninety seconds between each set [31]. Resistance training improves muscular strength by both neural and hypertrophic factors which lead to an increase in force production [32,33]. In addition, resistance training increases muscle size [34,35] and muscle quality [36]. ...
The fire service suffers from high rates of cardiovascular disease and poor overall health, and firefighters often suffer fatal and non-fatal injuries while on the job. Most fatal injuries result from sudden cardiac death, while non-fatal injuries are to the musculoskeletal system. Previous works suggest a mechanistic link between several health and performance variables and injury risk. In addition, studies have suggested physical activity and nutrition can improve overall health and occupational performance. This review offers practical applications for exercise via feasible training modalities as well as nutritional recommendations that can positively impact performance on the job. Time-efficient training modalities like high-intensity interval training and feasible modalities such as resistance training offer numerous benefits for firefighters. Also, modifying and supplementing the diet and can be advantageous for health and body composition in the fire service. Firefighters have various schedules, making it difficult for planned exercise and eating while on shift. The practical training and nutritional aspects discussed in this review can be implemented on-shift to improve the overall health and performance in firefighters.
... Given the discrepancy between muscle mass and strength loss, it is likely that neuromuscular maladaptation is at least partially responsible for these observations. It has long been recognized that neural adaptations play a critical role in the initial stages of strength gains (Moritani & deVries, 1979), such as improved motor unit firing patterns, enhanced voluntary activation (VA), decreased coactivation of antagonist muscles, and increased corticospinal excitability and decreased inhibition (Gabriel et al., 2006;Kidgell et al., 2017). ...
Limb immobilization causes rapid declines in muscle strength and mass. Given the role of the nervous system in immobilization‐induced weakness, targeted interventions may be able to preserve muscle strength, but not mass, and vice versa. The purpose of this study was to assess the effects of two distinct interventions during 1 week of knee joint immobilization on muscle strength (isometric and concentric isokinetic peak torque), mass (bioimpedance spectroscopy and ultrasonography), and neuromuscular function (transcranial magnetic stimulation and interpolated twitch technique). Thirty‐nine healthy, college‐aged adults (21 males, 18 females) were randomized into one of four groups: immobilization only (n = 9), immobilization + action observation/mental imagery (AOMI) (n = 10), immobilization + neuromuscular electrical stimulation (NMES) (n = 12), or control group (n = 8). The AOMI group performed daily video observation and mental imagery of knee extensions. The NMES group performed twice daily stimulation of the quadriceps femoris. Based on observed effect sizes, it appears that AOMI shows promise as a means of preserving voluntary strength, which may be modulated by neural adaptations. Strength increased from PRE to POST in the AOMI group, with +7.2% (Cohen's d = 1.018) increase in concentric isokinetic peak torque at 30°/s. However, NMES did not preserve muscle mass. Though preliminary, our findings highlight the specific nature of clinical interventions and suggest that muscle strength can be independently targeted during rehabilitation. This study was prospectively registered: ClinicalTrials.gov NCT05072652.
... Despite this, little is known about the physiological effects of this type of exercise. Most studies in this direction are related to neuromuscular functional responses and morphological changes (Abe et al., 2000;Finer et al., 1994;Garfinkel & Cafarelli, 1992;Moritani & Devries, 1979), nevertheless, few studies explore biochemical changes (Tamaki et al., 1992). According to Gaspersic et al. (1999), despite acetylcholinesterase (AChE) is a key enzyme in the regulation of neuromuscular junction (NMJ) activity, there is a scarcity of information in the literature about the changes in its activity caused by IST. ...
Introduction: Isometric strength training (IST) is an important component of different types of sport and others activities of daily life. However, until the present moment, no studies have linked the isometric strength training with acetylcholinesterase (AChE) activity changes. Objective: We evaluated the effects of IST on the muscular AChE activity and strength. Materials and Methods: Wistar rats (n =20) were divided into 2 groups: Control group (Ctr) (sedentary) and trained group (Tr) (submitted to 8 weeks of Isometric strength training). The muscle strength and the acetylcholinesterase activity were evaluated in the solear (SOL) and Extensor Digitorum Longus (EDL) muscles. Results: The body weight of the trained animals was 7.39 % lower than in Ctr rats (p < 0.01) and the EDL weight was 25 % higher (p < 0.05) compared to Ctr. Further, an increase of 30.36 % in strength was observed in the fourth week (p < 0.006) and 26.41 % in eighth week (p < 0.003) of training. In addition, we found an increase of 46.64% in AChE activity in the SOL. In contrast, a reduction of 55.36% in AChE activity in the EDL was observed. Conclusion: Our findings indicate that biochemical, zoometric and functional changes can be evoked by IST with low overload.
Keywords: Isometric Strength Training, Solear, Extensor Digitorum Longus and Enzyme.
... The cause of this variance remains uncertain, whether it is natural variability, issues with test-retest reliability, fatigue, or learning effects. Strength gains likely resulted from both neural adaptations and hypertrophy [56][57][58][59][60], with studies indicating similar hypertrophy changes in HL and LL conditions when effort (proximity to failure) and volume (number of working sets) are equated [47,54,61], emphasizing the significance of load in maximizing dynamic strength in experienced individuals [47]. ...
A total of nineteen elite youth cross-country skiers (16 ± 2 years) were divided into three groups: a low-load group (LL, n = 6) performing 15–20 repetitions per exercise, a high-load group (HL, n = 9) executing 6–12 repetitions, and a control group (CON, n = 4) exclusively engaging in endurance training. Testing included 1RM in upper-body exercises, VO2max running tests, and double-poling (DP) ergometer exhaustion and sprint tests to determine peak oxygen uptake (VO2peak-DP) and peak power (PP). The results indicated that HL and LL showed significant increases in VO2peak-DP, both in absolute values (d = −1.2 and −1.2, p < 0.05) and when normalized to body mass (d = 0.93 and 1.3, p < 0.05). Although there were no group*time effects for VO2peak-DP, PP during DP tests to exhaustion increased in both HL (d = −1.6, p < 0.05) and LL (d = 1.4, p < 0.05) compared to CON. Standardized to body mass, only HL showed significant improvements in PP during the sprint test (d = 1.7, p < 0.05). During the sprint test, both absolute and body-mass-normalized peak power increased only in the high-load group (d = −1.0 and 0.93, p < 0.05). In conclusion, high-load resistance training resulted in the greatest improvements in strength, DP performance, and VO2peak-DP, indicating a dose–response relationship to the load magnitude of resistance training.
... It is widely accepted that muscle hypertrophy typically occurs after at least 6 to 8 weeks of consistent resistance training (8), However, resistance training-induced muscle strength enhancement can occur in a shorter period of less than 6 weeks. This is believed to be primarily due to neuromuscular adaptations, rather than muscle hypertrophy (9,10). Nonetheless, resistance training can lead to early muscular biomolecular changes in the form of protein expression or at the level of either DNA or mRNA within the first week of training (11)(12)(13). ...
The molecular mechanisms underlying muscular adaptations to concentric (CON) and eccentric (ECC) exercise training have been extensively explored. However, most previous studies have focused on specifically selected proteins, thus, unable to provide a comprehensive protein profile and potentially missing the crucial mechanisms underlying muscular adaptation to exercise training. We herein aimed to investigate proteomic profiles of human skeletal muscle in response to short-term resistance training. Twenty young males were randomly and evenly assigned to two groups to complete a 4-week either ECC or CON training program. Measurements of body composition and physiological function of the quadriceps femoris were conducted both before and after the training. Muscle biopsies from the vastus lateralis of randomly selected participants (five in ECC and four in CON) of both before and after the training were analyzed using the liquid-chromatography tandem mass spectrometry in combination with bioinformatics analysis. Neither group presented a significant difference in body composition or leg muscle mass; however, muscle peak torque, total work, and maximal voluntary contraction were significantly increased after the training in both groups. Proteomics analysis revealed 122 differentially abundant proteins (DAPs; p value < 0.05 & fold change >1.5 or <0.67) in ECC, of which the increased DAPs were mainly related to skeletal muscle contraction and cytoskeleton and enriched specifically in the pentose phosphate pathway, extracellular matrix–receptor interaction, and PI3K−Akt signaling pathway, whereas the decreased DAPs were associated with the mitochondrial respiratory chain. One hundred one DAPs were identified in CON, of which the increased DAPs were primarily involved in translation/protein synthesis and the mitochondria respiratory, whereas the decreased DAPs were related to metabolic processes, cytoskeleton, and de-ubiquitination. In conclusion, the 4-week CON and ECC training resulted in distinctly different proteomic profiles, especially in proteins related to muscular structure and metabolism.
... Neural adaptations may be more in uential early in the 1-3-week period, whereas, after 4 weeks, an increase in explosive power is essential owing to changes in the muscle CSA. Based on this, Moritani et al. 34 found that the CSA of muscle bers and the motor unit recruitment ability contributed almost equally to muscle strength after 3-5 weeks of training. This may explain why we did not observe a difference in explosive power between the two groups after the 5-week training. ...
Introduction: The ability of the lower limbs to undergo high-velocity contractions significantly impacts the capacity of athletes. However, not much is known about the effect of drop-set training (DST) on muscle contraction velocity. This study aimed to examine the impact of rapid drop set resistance training on high-velocity lower extremity contractions.
Methods: Sixteen teenagers were assigned to either traditional resistance training (TRT) or DST groups. The TRT group performed squats at 1.8 times their body weight, while the DST group performed squats at 1.8 then 1.3 times their body weight. Before and after training, knee muscle strength and body composition were measured using an isokinetic dynamometer and bioelectrical impedance tester.
Results: There were significant increases in fat-free mass, peak torque at 180°/s, and peak work in the right leg of the DST group. Peak torque, peak work, and average power increased significantly post-intervention butdid not differ significantly between the two groups.
Conclusion: Compared to constant resistance training, 1.8- and 1.3-times body weight drop training is more effective than constant resistance training in boosting muscle mass and strength during rapid contractions of the lower extremities. Furthermore, both TRT and DST effectively improve lower-extremity muscle strength at lower-speed contractions.
... This combined information can also be used to calculate corrected girth values (which account for an adjustment of skinfold thickness to determine musculoskeletal cross-sectional area) or lean mass index (a log-based adjustment for body mass and summed skinfolds) [94] . Notably, DeFreitas et al. [95] demonstrated that, despite underestimating muscle cross-sectional area compared to peripheral quantitative computed tomography (pQCT), both a corrected girth equation [96] and a regression equation [97] adequately tracked changes in this value during an eight-week resistance training program. A recent review by Duarte et al. [98] discusses numerous validated anthropometric equations for limb-specific muscle mass estimation. ...
Skeletal muscle is the largest organ system in the human body and plays critical roles in athletic performance, mobility, and disease pathogenesis. Despite growing recognition of its importance by major health organizations, significant knowledge gaps remain regarding skeletal muscle health and its crosstalk with nearly every physiological system. Relevant public health challenges like pain, injury, obesity, and sarcopenia underscore the need to accurately assess skeletal muscle health and function. Feasible, non-invasive techniques that reliably evaluate metrics including muscle pain, dynamic structure, contractility, circulatory function, body composition, and emerging biomarkers are imperative to unraveling the complexities of skeletal muscle. Our concise review highlights innovative or overlooked approaches for comprehensively assessing skeletal muscle in vivo. We summarize recent advances in leveraging dynamic ultrasound imaging, muscle echogenicity, tensiomyography, blood flow restriction protocols, molecular techniques, body composition, and pain assessments to gain novel insight into muscle physiology from cellular to whole-body perspectives. Continued development of precise, non-invasive tools to investigate skeletal muscle are critical in informing impactful discoveries in exercise and rehabilitation science.
... For example, the results are used to understand the development levels of children's physical functions (Lesinski et al. 2020;Tambalis et al. 2011), degree of locomotor dysfunction in older adults or patients (Burton et al. 2013;Yamada et al. 2017;Kimura et al. 2012), and the effects of exercise interventions (Lopez et al. 2018 fitness tests has not been fully clarified. It is well-known that physical functions or performances are mainly determined by morphological and neural factors, i.e., muscle volume/ quality and central nervous control (Balshaw et al. 2017; Moritani and deVries 1979). The ability to quantify the components of individual physical fitness tests from these factors would provide useful information to interpret the results of such tests. ...
Purpose
While various fitness tests have been developed to assess physical performances, it is unclear how these tests are affected by differences, such as, in morphological and neural factors. This study was aimed to investigate associations between individual differences in physical fitness tests and neuromuscular properties.
Methods
One hundred and thirty-three young adults participated in various general physical fitness tests and neuromuscular measurements. The appendicular skeletal muscle mass (ASM) was estimated by bioelectrical impedance analysis. Echo intensity (EI) was evaluated from the vastus lateralis. During submaximal knee extension force, high-density surface electromyography of the vastus lateralis was recorded and individual motor unit firings were detected. Y-intercept (i-MU) and slope (s-MU) from the regression line between the recruitment threshold and motor unit firing rate were calculated.
Results
Stepwise multiple regression analyses revealed that knee extension strength could be explained (adjusted R² = 0.712) by ASM (β = 0.723), i-MU (0.317), EI (− 0.177), and s-MU (0.210). Five-sec stepping could be explained by ASM (adjusted R² = 0.212). Grip strength, side-stepping, and standing broad jump could be explained by ASM and echo intensity (adjusted R² = 0.686, 0.354, and 0.627, respectively). Squat jump could be explained by EI (adjusted R² = 0.640). Counter-movement jump could be explained by EI and s-MU (adjusted R² = 0.631). On the other hand, i-MU and s-MU could be explained by five-sec stepping and counter-movement jump, respectively, but the coefficients of determination were low (adjusted R² = 0.100 and 0.045).
Conclusion
Generally developed physical fitness tests were mainly explained by morphological factors, but were weakly affected by neural factors involved in performance.
... Both legs demonstrated a gradual increase in muscle strength (∼10% over 12 days in maximal ankle joint moment and AT force; Fig. 3) suggesting that the rest periods did not lead to clear fatigue for the ankle plantar flexors irrespective of differences in total loading volume. This rapid increase in muscle strength could be explained as predominantly a neural adaptation (Moritani and DeVries, 1979). Accordingly, one might suggest that the regeneration of muscular performance capacity has surpassed the recovery processes in tendinous tissues in both legs (Magnusson et al., 2010). ...
In response to a mechanical stimulus, tendons have a slower tissue renewal rate compared to muscles. This could over time lead to a higher mechanical demand (experienced strain) for the tendon, especially when a high strain magnitude exercise is repeated without sufficient recovery. The current study investigated the adaptive responses of the triceps surae (TS) muscle-tendon unit (MTU) and extracellular matrix turnover-related biomarkers to repetitive high tendon strain cyclic loading. Eleven young male adults performed a progressive resistance exercise over 12 consecutive days, consisting of high Achilles tendon (AT) strain cyclic loading (90% MVC) with one leg once a day (LegT1) and the alternate leg three times a day (LegT3). Exercise-related changes in TS MTU mechanical properties and serum concentrations of extracellular matrix turnover-related biomarkers were analysed over the intervention period. Both legs demonstrated similar increases in maximal AT force (∼10%) over the 12-day period of exercise. A ∼20% increase in maximal AT strain was found for LegT3 (p<0.05) already after 8 consecutive exercise days, along with a corresponding decrease in AT stiffness. These effects were maintained even after a 48h rest period. The AT mechanical properties for LegT1 were unaltered. Biomarker analysis revealed no sign of inflammation, but altered collagen turnover and delayed increase in the collagen type I synthesis rate. Accordingly, we suggest that tendon is vulnerable to frequent high-magnitude and volume of cyclic mechanical loading, as accumulation of micro-damage can potentially exceed the rate of biological repair, leading to increased maximal tendon strain.
... [28,29] According to a neural factor theory, it has been reported that repeated training of at least 4 weeks is required to increase the thickness and strength of skeletal muscles before a change can be confirmed. [30] Based on the experimental protocol and theory of these previous studies, resistive swallowing exercises using KT for 6 weeks were performed in this study to induce changes in the myophysiology of the suprahyoid muscles. The results of this study are consistent with those of previous studies. ...
Background
Recently, swallowing resistive exercise using kinesiology taping (KT) has been reported as a novel method for dysphagia rehabilitation However, clinical evidence is still unclear, and effects in the elderly have not been confirmed.
Objective
This study aimed to investigate the effects of suprahyoid muscle strengthening exercise using KT on muscle activation and thickness in community-dwelling elderly.
Methods
A total of 24 healthy older people were enrolled in this study and randomly assigned to an experimental group and a placebo group. In the experimental group, KT was attached to the front of the neck with a tension of about 70% to 80%, and a resistive swallowing exercise was performed. In the placebo group, the tape was applied similarly but without tension. Both groups performed resistive swallowing exercises 10 times a day (50 swallows per day) for 6 weeks. The activation and thickness of the suprahyoid muscles were measured using portable ultrasound equipment and an surface electromyelograph device.
Results
The experimental group showed a significant increase in suprahyoid muscle activation (mean and peak) and muscle thickness (digastric and mylohyoid) than the placebo group (all, P < .05).
Conclusion
This study confirmed that suprahyoid muscle strengthening exercise using KT had a positive effect on the suprahyoid muscles in healthy older adults, thus suggesting the possibility of a therapeutic exercise method for dysphagia rehabilitation.
Background: Parkinson's disease, with its evolution, leads to progressive disorders that compromise the functional mobility of the affected individuals. The whole body vibration as a rehabilitation tool seems to be a promising alternative in Parkinson's disease. Objective: The aim of this study was to verify the effect of VCT on functional mobility and quality of life in individuals with Parkinson's disease. Methods: Ten individuals (four men and six women) diagnosed with Parkinson's disease were evaluated before and after a protocol of 10 training sessions on a vibrating platform using the Short Physical Performance Battery (SPPB) in the domains: balance, gait, limb strength and Parkinson's Disease Questionnaire -PDQ39. The pre and post-intervention data were compared using the using the ANOVA test for repeated and post-hoc Bonferroni measurements (p <0.05). Results: Those evaluated had an average age of 70.00 ± 9.68 years and an average disease evolution time of 3.38 ± 1.51 years. The whole body vibration increased the SPPB scores in all domains: balance (10%), gait (31%), lower limbs (35%) and total strength (23%), and reduced the total scores of the PDQ- 39 (23%). Conclusions: It was concluded that the suggested vibration protocol was able to improve the functional capacity and quality of life of individuals with Parkinson's disease.
Improving performance in strength tasks requires modifications characteristic of motor skill learning, such as more efficacious motor-unit firing behavior. Because domain-specific knowledge is integral to learning and performing motor skills, the present purpose was to examine selected factors of strength-specific knowledge and effects they might have on acquiring strength. Following baseline testing for maximal strength on a knee-extension task, participants were matched by sex and strength and placed into control (n = 8) and treatment (n = 8) groups. Quadriceps muscle electromyographic data were also collected. The treatment group underwent two educational sessions detailing muscle physiology, neural control of muscle force, and imagery training using this knowledge. The control group underwent two educational sessions about health and fitness. Following the educational sessions the participants were retested for strength. Analysis indicated that the education and imagery treatment had no effect on strength, nor did electromyographic measures indicate that the treatment group benefitted from intervention. It was concluded that the knowledge was simply not relevant to knee extension-force production or that use of the knowledge involved a disadvantageous internal focus of attention away from relevant task demands.
The arterial switch operation (ASO) remains the gold standard of care for neonates with transposition of great arteries (TGA). However, the timing and the choice of surgical procedure in children presenting late with transposition of great arteries with intact ventricular septum (TGA/IVS) and regressed left ventricle (rLV) is still a matter of debate. Evolution of the concept of left ventricular re-training with different techniques has led to a paradigm shift in the management of this subset of late presenting ‘simple’ transposition.
Literature review was done in Pubmed and Scopus to identify relevant articles pertaining to the pathophysiology and different treatment options for late presenting TGA with intact ventricular septum with an aim of writing a review on the subject.
Multiple treatment options have been reported in the literature varying from a single-stage operation to multi-stage procedure to achieve good long-term result. Majority are isolated case reports or case series with small number of children and only few studies have mid-term and long-term outcomes.
In children presenting late with TGA and rLV, left ventricular re-training seems the most feasible and effective method. In hospital setups with cost constraints, other low-risk techniques can be attempted but corrective surgery will be needed in the future, thus making these procedures cost-shifting strategies rather than cost-saving procedures.
Dear students, future cosmetologists,
The teaching material we present uses data from research and websites on current topics in the field of aesthetics and cosmetology such as anti-aging treatments, skin rejuvenation, body shaping and fat reduction, tattoo removal as well as treatments for slimming and body shaping. These are primarily new insights based on the application of hardware devices used in cosmetology practice around the world. In each separate topic, the indications, the necessary qualifications and permits for the use of the device, the method of dosing, the side effects and all that are based on medical documentation from published professional papers are processed.
Medical science is clearly moving forward, we must follow new knowledge, both in terms of effects and side effects when applying certain cosmetic treatments. As uncommercial as it may seem, medical ethics should be observed when applying these treatments. Guided by the principle of doing no harm, we are moving forward towards the application of ethics on a scientific basis.
Every research offers new dimensions in our practical work, this textbook offers just that, education for medical persons, education for practitioners and facts for education for clients, because not everything presented is always harmless.
Sarcopenia refers to a neuromuscular disease characterized by age-related declines in muscle mass and function. Since Professor Rosenberg first introduced the concept of sarcopenia in 1989, numerous operational paradigms have been proposed, tested, and validated against negative outcomes. The most recent recommendations advocate that dynapenia, or reduced of muscle strength, should be used alongside low muscle mass for the identification of sarcopenia. This approach is based on the understanding that impairments in muscle strength are a major consequence of muscle failure. However, empirical evidence has yielded conflicting results regarding the ability of current sarcopenia definitions to identify individuals at higher risk of adverse health-related events. Muscle power — the capacity to generate strength rapidly — has emerged as a critical domain of physical performance in old age. Not only does it decline earlier and more drastically than other measures (e.g., muscle strength), but it is also more strongly associated with adverse outcomes. In this view point, we provide an appraisal of muscle power as a more reliable indicator of muscle failure, compared with other measures (e.g., strength), for identifying individuals with sarcopenia in both geriatric and non-geriatric settings. We also discuss major challenges hindering the conduct of meaningful investigations on this subject.
The aim of this study was to investigate how lifting straps affect isometric back extensors muscle strength. The participants were divided according to gender and training level: trained – powerlifters (n = 17) and control – a specifically non-trained group (n = 24). For the purposes of this study, the maximum voluntary contraction of the back extensors was measured in isometric conditions in the isometric back extension exercise. After a 5-minute standard and specific warm-up, the participants had three trials each with lifting straps and without lifting straps, with a break of 2 minutes between trials. They were given the verbal instruction "pull as hard and fast as possible” and hold for 2 to 3 seconds. Repeated measures ANOVA showed a general statistically significant difference (p<0.05) between testing procedures (classical and straps). A paired samples t-test was used to determine differences between maximal and explosive strength variables. Then, the percentage difference (Δ) of all variables (Fmax - maximal force, RFDmax - maximal rate of force development, tFmax - time needed to reach maximal force, tRFDmax - time for maximal rate of force development) was calculated using the formula: Fmax_Δ = ((Fmax_straps - Fmax_class) / Fmax_class) *100. Differences in the maximum isometric back extension force (Fmax) were found in both groups (powerlifter males - p = 0.004, females - p = 0.019 and control group males - p = 0.018, females – p = 0.001), while differences in tFmax were observed only in the control group (males – p = 0.001 and females - p = 0.000). The results showed that lifting straps have a positive effect in measuring supra-maximal isometric strength (averaged enhancement was 15.93±4.58% regardless of gender and training status), and can potentially be used in a methodological sense to determine the objective values.
Range of motion in exercises is one of the foundations for greater activation of a muscle group. The objective of this investigation was to compare the structural and functional capacity of the triceps brachii between three groups with different angles (90°, 110°, and 130°) in a unilateral elbow extension exercise. The sample consisted of 25 subjects with a mean age of 24.12 ± 3.83 years, mean height of 1.78 ± 0.10 m and mean body weight of 78.01 ± 15.70 kg. The following variables were collected pre-and post-intervention: triceps brachii circumference, one repetition maximum, and electromyography during dynamic exercise. Over eight weeks, subjects performed this exercise, performing 3 sets of 12 repetitions for each arm, with days of rest in between. The results showed that the 110° angle provided greater muscle activation compared to the other angles. There was no difference between the triceps brachii circumference and the root mean square (RMS) between the groups. It was concluded that, although the 110º angle showed a tendency for greater muscle activation, the RMS and arm perimeter data did not show significant differences between all the angles evaluated (90º, 110º, 130º). 446 AIMS Biophysics Volume 11, Issue 4, 445−454.
Background
The optimal prescription and precise recommendations of resistance training volume for older adults is unclear in the current literature. In addition, the interactions between resistance training volume and program duration as well as physical health status remain to be determined when assessing physical function, muscle size and hypertrophy and muscle strength adaptations in older adults.
Objectives
This study aimed to determine which resistance training volume is the most effective in improving physical function, lean body mass, lower-limb muscle hypertrophy and strength in older adults. Additionally, we examined whether effects were moderated by intervention duration (i.e. short term, < 20 weeks; medium-to-long term, ≥ 20 weeks) and physical health status (i.e. physically healthy, physically impaired, mixed physically healthy and physically impaired; PROSPERO identifier: CRD42023413209).
Methods
CINAHL, Embase, LILACS, PubMed, Scielo, SPORTDiscus and Web of Science databases were searched up to April 2023. Eligible randomised trials examined the effects of supervised resistance training in older adults (i.e. ≥ 60 years). Resistance training programs were categorised as low (LVRT), moderate (MVRT) and high volume (HVRT) on the basis of terciles of prescribed weekly resistance training volume (i.e. product of frequency, number of exercises and number of sets) for full- and lower-body training. The primary outcomes for this review were physical function measured by fast walking speed, timed up and go and 6-min walking tests; lean body mass and lower-body muscle hypertrophy; and lower-body muscle strength measured by knee extension and leg press one-repetition maximum (1-RM), isometric muscle strength and isokinetic torque. A random-effects network meta-analysis was undertaken to examine the effects of different resistance training volumes on the outcomes of interest.
Results
We included a total of 161 articles describing 151 trials (n = 6306). LVRT was the most effective for improving timed up and go [− 1.20 standardised mean difference (SMD), 95% confidence interval (95% CI): − 1.57 to − 0.82], 6-min walk test (1.03 SMD, 95% CI: 0.33–1.73), lean body mass (0.25 SMD, 95% CI: 0.10–0.40) and muscle hypertrophy (0.40 SMD, 95% CI: 0.25–0.54). Both MVRT and HVRT were the most effective for improving lower-limb strength, while only HVRT was effective in increasing fast walking speed (0.40 SMD, 95% CI: − 0.57 to 0.14). Regarding the moderators, our results were independent of program duration and mainly observed for healthy older adults, while evidence was limited for those who were physically impaired.
Conclusions
A low resistance training volume can substantially improve healthy older adults’ physical function and benefits lean mass and muscle size independently of program duration, while a higher volume seems to be necessary for achieving greater improvements in muscle strength. A low volume of resistance training should be recommended in future exercise guidelines, particularly for physically healthy older adults targeting healthy ageing.
We aimed to implement strength and balance training for elite adolescent male soccer players with functional ankle instability (FAI) to assess kinesiophobia, ankle instability, ankle function, and performance. This cluster randomized controlled trial comprised 51 elite adolescent male soccer players with FAI recruited from six different teams, divided into strength, balance, and control groups (SG, n = 17; BG, n = 17; and CG, n = 17, respectively). The SG and BG underwent strength and balance training sessions three times per week for 6 weeks. Primary outcomes were the Tampa scale for kinesiophobia-17 (TSK) and Cumberland ankle instability tool (CAIT) scores to assess kinesiophobia and FAI, respectively. Secondary outcomes were ankle strength (four directions), dynamic balance, static balance (ellipse, displacement, velocity), and performance (figure 8 and side-hop tests). A significant interaction effect was observed for both TSK and CAIT post-intervention (both, P < 0.01). In post hoc analyses, the BG had significantly better outcomes in reducing TSK. The SG and BG showed greater improvements in CAIT scores. Regression analysis indicated that CAIT severity correlated significantly with TSK (P = 0.039, R = 0.289). For secondary outcomes, the SG and BG were superior in terms of ankle dorsiflexion/inversion strength, static balance displacement, and figure-8 and side-hop tests (all, P < 0.05). The BG showed significantly better static balance ellipse results (P < 0.05). The 6-week intervention significantly enhanced kinesiophobia management, ankle stability, and performance. Balance training effectively mitigated kinesiophobia and improved balance, compared with strength training alone. Even small variations in CAIT severity can influence kinesiophobia, highlighting the potential benefits of balance training. Integrating balance training into training programs can address both physical and psychological aspects of ankle instability. Research is recommended to explore the longitudinal effects of these interventions and their potential to prevent injury recurrence.
Background:
High-density surface electromyography (HD-sEMG) has enabled non-invasive analysis of motor unit (MU) activity and recruitment, but its application to swallowing-related muscles is limited.
Objective:
We aimed to investigate the utility of HD-sEMG for quantitatively evaluating the MU recruitment characteristics of the suprahyoid muscles during tongue elevation.
Methods:
We measured the sEMG activity of the suprahyoid muscles of healthy participants during tongue elevation using HD-sEMG. Maximum voluntary contraction (MVC) was measured, followed by data collection during sustained and ramp-up tasks to capture suprahyoid muscle activity. Changes in the temporal/spatial MU recruitment patterns within individual suprahyoid muscles were analysed.
Results:
This study enrolled 16 healthy young adults (mean age: 27.8 ± 5.3 years; eight males and eight females). Increasing muscle force corresponded to a decrease in modified entropy and correlation coefficient and an increase in the coefficient of variation. No significant differences were observed between male and female participants.
Conclusion:
The results of this study, consistent with those observed in other muscles, such as the vastus lateralis muscle, suggest that HD-sEMG is a valuable and reliable tool for quantitatively evaluating MU recruitment in the suprahyoid muscles. This measurement technique holds promise for novel assessments of swallowing function.
High Responders to Hypertrophic Strength Training Also Tend to Lose More Muscle Mass and Strength During Detraining Than Low Responders: Erratum
Räntilä, Aapo; Ahtiainen, Juha P.; Avela, Janne; Restuccia, Joel; Kidgell, Dawson; Häkkinen, Keijo
Journal of Strength and Conditioning Research 38(4):p 63
In the article “High Responders to Hypertrophic Strength Training Also Tend to Lose More Muscle Mass and Strength During Detraining Than Low Responders”,1 which published in Volume 35, Issue 6 of the Journal of Strength & Conditioning Research, there are minor typographical errors in Figure 2, which are now corrected.
Quantifying skeletal muscle size is necessary to identify those at risk for conditions that increase frailty, morbidity, and mortality, as well as decrease quality of life. Although muscle strength, muscle quality, and physical performance have been suggested as important assessments in the screening, prevention, and management of sarcopenic and cachexic individuals, skeletal muscle size is still a critical objective marker. Several techniques exist for estimating skeletal muscle size; however, each technique presents with unique characteristics regarding simplicity/complexity, cost, radiation dose, accessibility, and portability that are important factors for assessors to consider before applying these modalities in practice. This narrative review presents a discussion centred on the theory and applications of current non‐invasive techniques for estimating skeletal muscle size in diverse populations. Common instruments for skeletal muscle assessment include imaging techniques such as computed tomography, magnetic resonance imaging, peripheral quantitative computed tomography, dual‐energy X‐ray absorptiometry, and Brightness‐mode ultrasound, and non‐imaging techniques like bioelectrical impedance analysis and anthropometry. Skeletal muscle size can be acquired from these methods using whole‐body and/or regional assessments, as well as prediction equations. Notable concerns when conducting assessments include the absence of standardised image acquisition/processing protocols and the variation in cut‐off thresholds used to define low skeletal muscle size by clinicians and researchers, which could affect the accuracy and prevalence of diagnoses. Given the importance of evaluating skeletal muscle size, it is imperative practitioners are informed of each technique and their respective strengths and weaknesses.
Jumping and landing activities are the most common mechanism of injury in professional ballet dancers. There is limited evidence, however, that has elucidated the moderators of load experienced when jumping and landing in ballet. This thesis aimed to describe injury epidemiology, establish reliable methods of assessing strength and jumping, and explore the factors that may influence lower extremity load during jump landings in professional ballet dancers.
A five-year injury epidemiology study revealed an incidence of medical attention and time-loss injuries of ~3–4 and ~1 per 1000 h of exposure, respectively. The mechanism of injury was jumping and landing activities in ~30–40% of time loss injuries. A systematic review found limited evidence that ballet dancers demonstrate externally rotated lower extremities, extended lower extremities prior to landing, and ankle-dominant jumping strategies.
Two methodological studies established the within- and between-session reliability of vertical ground reaction force (vGRF) across several maximal isometric force tests and three-dimensional ankle mechanics during landing in turnout and parallel foot positions. The reliability of vGRF during maximal isometric force tests across the squat, standing plantarflexion, and seated plantarflexion positions demonstrated excellent reliability (intraclass correlation coefficients (ICC): 0.92–1.00) and low variability (coefficient of variation (CV): 2.0–6.5%). Three-dimensional ankle mechanics demonstrated within- (ICC: 0.17–0.96; CV: 1.4¬–82.3%) and between-session (ICC: 0.02–0.98; CV:1.3–57.1%) reliability ranging from poor to excellent, with, ankle excursion, peak ankle angle, and jump height demonstrating the greatest ICC values (ICC: 0.65–0.96; CV: 1.4–57%).
The final two studies investigated jump landings in professional ballet dancers. A linear discriminate analysis revealed that three-dimensional ankle mechanics could discriminate different ballet foot positions, such that jump landings in fourth and fifth positions required a greater range of motion and ankle joint power when compared to other foot positions. Lastly, two linear mixed-effects models indicated that peak ankle joint moments and vGRFs have poor associations with strength, ankle dorsiflexion range of motion, and three-dimensional ankle excursions (R2: 0.01–0.02). Sex, foot position, and individual variation are more appropriate factors to consider when assessing the load experienced at a joint or system level.
This thesis provides a thorough insight into injury, strength, and jumping in professional ballet dancers. To that end, this thesis has identified burdensome injuries and their mechanisms in professional ballet dancers alongside practical and reliable strategies to measure the physical attributes that may moderate the load experienced by a dancer upon landing.
The risk associated with multiple cancers, cardiovascular disease, diabetes, and all-cause mortality is decreased in individuals who meet the current recommendations for physical activity. Therefore, regular exercise remains a cornerstone in the prevention and treatment of non-communicable diseases. An acute bout of exercise results in the coordinated interaction between multiple tissues to meet the increased energy demand of exercise. Over time, the associated metabolic stress of each individual exercise bout provides the basis for long-term adaptations across tissues, including the cardiovascular system, skeletal muscle, adipose tissue, liver, pancreas, gut, and brain. Therefore, regular exercise is associated with a plethora of benefits throughout the whole body, including improved cardiorespiratory fitness, physical function, and glycemic control. Overall, we summarize the exercise-induced adaptations that occur within multiple tissues and how they converge to ultimately improve cardiometabolic health.
The limb position effect is a multi-faceted problem, associated with decreased upper-limb prosthesis control acuity following a change in arm position. Factors contributing to this problem can arise from distinct environmental or physiological sources. Despite their differences in origin, the effect of each factor manifests similarly as increased input data variability. This variability can cause incorrect decoding of user intent. Previous research has attempted to address this by better capturing input data variability with data abundance. In this paper, we take an alternative approach and investigate the effect of reducing trial-to-trial variability by improving the consistency of muscle activity through user training. Participants underwent 4 days of myoelectric training with either concurrent or delayed feedback in a single arm position. At the end of training participants experienced a zero-feedback retention test in multiple limb positions. In doing so, we tested how well the skill learned in a single limb position generalized to untrained positions. We found that delayed feedback training led to more consistent muscle activity across both the trained and untrained limb positions. Analysis of patterns of activations in the delayed feedback group suggest a structured change in muscle activity occurs across arm positions. Our results demonstrate that myoelectric user-training can lead to the retention of motor skills that bring about more robust decoding across untrained limb positions. This work highlights the importance of reducing motor variability with practice, prior to examining the underlying structure of muscle changes associated with limb position.
Background
Running economy is defined as the energy demand at submaximal running speed, a key determinant of overall running performance. Strength training can improve running economy, although the magnitude of its effect may depend on factors such as the strength training method and the speed at which running economy is assessed.
Aim
To compare the effect of different strength training methods (e.g., high loads, plyometric, combined methods) on the running economy in middle- and long-distance runners, over different running speeds, through a systematic review with meta-analysis.
Methods
A systematic search was conducted across several electronic databases including Web of Science, PubMed, SPORTDiscus, and SCOPUS. Using different keywords and Boolean operators for the search, all articles indexed up to November 2022 were considered for inclusion. In addition, the PICOS criteria were applied: Population: middle- and long-distance runners, without restriction on sex or training/competitive level; Intervention: application of a strength training method for ≥ 3 weeks (i.e., high loads (≥ 80% of one repetition maximum); submaximal loads [40–79% of one repetition maximum); plyometric; isometric; combined methods (i.e., two or more methods); Comparator: control group that performed endurance running training but did not receive strength training or received it with low loads (< 40% of one repetition maximum); Outcome: running economy, measured before and after a strength training intervention programme; Study design: randomized and non-randomized controlled studies. Certainty of evidence was assessed with the GRADE approach. A three-level random-effects meta-analysis and moderator analysis were performed using R software (version 4.2.1).
Results
The certainty of the evidence was found to be moderate for high load training, submaximal load training, plyometric training and isometric training methods and low for combined methods. The studies included 195 moderately trained, 272 well trained, and 185 highly trained athletes. The strength training programmes were between 6 and 24 weeks’ duration, with one to four sessions executed per week. The high load and combined methods induced small (ES = − 0.266, p = 0.039) and moderate (ES = − 0.426, p = 0.018) improvements in running economy at speeds from 8.64 to 17.85 km/h and 10.00 to 14.45 km/h, respectively. Plyometric training improved running economy at speeds ≤ 12.00 km/h (small effect, ES = − 0.307, p = 0.028, β1 = 0.470, p = 0.017). Compared to control groups, no improvement in running economy (assessed speed: 10.00 to 15.28 and 9.75 to 16.00 km/h, respectively) was noted after either submaximal or isometric strength training (all, p > 0.131). The moderator analyses showed that running speed (β1 = − 0.117, p = 0.027) and VO2max (β1 = − 0.040, p = 0.020) modulated the effect of high load strength training on running economy (i.e., greater improvements at higher speeds and higher VO2max).
Conclusions
Compared to a control condition, strength training with high loads, plyometric training, and a combination of strength training methods may improve running economy in middle- and long-distance runners. Other methods such as submaximal load training and isometric strength training seem less effective to improve running economy in this population. Of note, the data derived from this systematic review suggest that although both high load training and plyometric training may improve running economy, plyometric training might be effective at lower speeds (i.e., ≤ 12.00 km/h) and high load strength training might be particularly effective in improving running economy (i) in athletes with a high VO2max, and (ii) at high running speeds.
Protocol Registration
The original protocol was registered (https://osf.io/gyeku) at the Open Science Framework.
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“Budo and Science Concept”
Conceptualising kata as rehabilitation for para and disability karatedo and athletic performance, working memory, processing speed and cognitive reserve for persons living with acquired brain injury and spinal cord injury.
The purpose of this study was to examine the effects of a 4-week neuromuscular electrical stimulation (NMES) training regimen on involuntary torque output and electrical stimulation intensity in older adults. Twelve older adults (ages: 68.4 ± 6.5 years; men: n = 6, women: n = 6; weight: 158.6 ± 27.3 lbs; height: 65.2 ± 2.1 in) received submaximal intensity NMES to the quadriceps for 4 weeks to determine training-related changes in stimulation intensity and involuntary control of muscular torque during the NMES protocol. Two-way repeated measures ANOVAs were used to compare torque parameters and stimulation intensity between days and across protocol time bins. After training, stimulation intensity and torque increased over the course of the NMES protocol, while torque decreased during the protocol pre-training. These results suggest that muscular endurance of involuntary muscle contraction is increased with NMES training, and that stimulation intensity should be increased throughout the course of training to augment muscular torque output.
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