Figure 6 - uploaded by Hannah Dimmick
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Number of motor units recorded during each time at recruitment (T REC ) interval for females and males.
Source publication
Objective:
This study examined motor unit (MU) firing rates during a prolonged isometric contraction of the vastus lateralis (VL) for females and males.
Methods:
Surface electromyographic (sEMG) signals were recorded from the VL for eleven females and twelve males during a 45-second isometric trapezoid muscle actions at 40% of maximal voluntary...
Contexts in source publication
Context 1
... when accounting for recruitment threshold, Parra et al. 28 reported no sex-related differences in the MFR vs. RT relationships for the FDI at 10% MVC, and Peng et al. 31 found no differences in the vastus medialis at 30% MVC. For the present study, the difference between sexes observed in the grouped relationships could potentially be attributed to differences in sampling rather than the physiological characteristics of MUs ( Figure 6). Referring to Figure 6, there was a greater likelihood of recording MUs that were recruited earlier for the females (mean T REC =2.27±1.19 ...
Context 2
... the present study, the difference between sexes observed in the grouped relationships could potentially be attributed to differences in sampling rather than the physiological characteristics of MUs ( Figure 6). Referring to Figure 6, there was a greater likelihood of recording MUs that were recruited earlier for the females (mean T REC =2.27±1.19 seconds) than males (mean T REC =2.72±1.61 ...
Context 3
... when accounting for recruitment threshold, Parra et al. 28 reported no sex-related differences in the MFR vs. RT relationships for the FDI at 10% MVC, and Peng et al. 31 found no differences in the vastus medialis at 30% MVC. For the present study, the difference between sexes observed in the grouped relationships could potentially be attributed to differences in sampling rather than the physiological characteristics of MUs ( Figure 6). Referring to Figure 6, there was a greater likelihood of recording MUs that were recruited earlier for the females (mean T REC =2.27±1.19 ...
Context 4
... the present study, the difference between sexes observed in the grouped relationships could potentially be attributed to differences in sampling rather than the physiological characteristics of MUs ( Figure 6). Referring to Figure 6, there was a greater likelihood of recording MUs that were recruited earlier for the females (mean T REC =2.27±1.19 seconds) than males (mean T REC =2.72±1.61 ...
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This study aimed to investigate how facilitatory and inhibitory KT of the Vastus Medialis affected the activation and the fatigue indices of VM, Vastus Lateralis (VL) and Rectus Femoris (RF) throughout a dynamic fatigue protocol. Seventeen collegiate athletes (Ten males, seven females, age: 24.76 ± 3.99 years, height: 1.73 ± 0.10 m, mass: 68.11 ± 8...
Citations
... Although many studies have focused on muscle strength [17,19] and muscle activity [3,18,24], it is unclear whether the nervous system that coordinates them, especially the MU behavior (the smallest basic unit of movement), is changed in those with scapular dyskinesis. MU behavior is not always constant and varies with age [25,26], sex [27,28], and the presence of a musculoskeletal disorder [29,30], and those with scapular dyskinesis may also have characteristic MU behavior. ...
... Third, the sex ratio varied by group. Differences in MU behavior between the sexes have also been observed [27,28]. Sex differences in MU behavior in the lower trapezius and serratus anterior are unknown, but it is possible that differences in sex ratio may have in uenced the results. ...
Scapular dyskinesis results from weakness of the lower trapezius and serratus anterior, but no studies have investigated the motor unit (MU) behavior required for muscle exertion. This study aimed to classify scapular dyskinesis into raising (SDR) and lowering (SDL) phases and investigated the MU behaviors of the lower trapezius and serratus anterior. Fifty healthy young subjects underwent a scapular dyskinesis test and were divided into Normal, SDR, and SDL groups. The subjects performed submaximal voluntary contractions of the lower trapezius and serratus anterior, and surface electromyography signals were decomposed into the MU action potential amplitude (MUAP AMP ), mean firing rate (MFR), and recruitment threshold (RT). The average MUAP AMP and MFR and the slopes and y-intercepts of the linear MUAP AMP -RT and MFR-RT were compared. The MUAP AMP -RT slopes in the lower trapezius ( p = 0.049, r = 0.420) and serratus anterior were smaller ( p = 0.010, r = 0.490) and the MFR-RT y-intercept in the serratus anterior was lower ( p = 0.004, r = 0.540) in the SDR group than in the Normal group. Differences in other parameters between the SDL and Normal groups were not significant. Lower trapezius and serratus anterior MU behavioral changes may cause scapular dyskinesis in the raising phase.
... Several datasets that included equal numbers of males and females point to the possibility of sex differences in maximal or mean discharge rate in several muscles, including genioglossus muscle (Bailey et al., 2007), tibialis anterior Green and Gabriel, 2018;Hoshizaki et al., 2020), vastus lateralis or medialis (Knight and Kamen, 2008;Tucker et al., 2009), first dorsal interosseous (McManus et al., 2019) and flexor carpi radialis Hoshizaki et al., 2020). While sex differences were established in the tibialis anterior (Christie and Kamen, 2010;Inglis and Gabriel, 2020;Kowalski and Christie, 2020;Piasecki et al., 2021;Taylor et al., 2022), first dorsal interosseus Parra et al., 2020) and vastus lateralis or medialis (Dimmick et al., 2022;Guo et al., 2022;Peng et al., 2018), potential sex differences in flexor carpi radialis, biceps and triceps brachii, genioglossus and occipitofrontalis muscle should be investigated. ...
The lack of systematic investigations on sex-related differences in motor unit behaviour poses a challenge in understanding and optimizing health and performance in males and females. Limited investigations revealed that sex differences in motor unit behaviour might be present in human muscles. This review summarizes the current knowledge on sex differences in motor unit behaviour and potential factors that may contribute to these differences. We show significant under-representation of female participants in motor unit studies and a limited number of studies investigating sex differences in motor unit behaviour. We place the current insights within the context of methodological limitations and outline several recommendations and future directions to improve female representation in this research area. We conclude that there is an urgent need to gather more data in females and investigate sex differences in motor unit behaviour. The knowledge gained could be used to develop sex-specific approaches to improve neuromuscular performance and rehabilitation.
Resistance exercise training (RET) is a key modality to enhance sports performance, injury prevention and rehabilitation, and improving overall health via increases in muscular strength. Yet, the contribution of neural mechanisms to increases in muscular strength are highly debated. This is particularly true for the involvement of the motor unit, which is the link between neural (activation) and mechanical (muscle fiber twitch forces) mechanisms. A plethora of literature that examines the effects of RET on skeletal muscle speculate the role of motor units, such as increases in firing rates partially explains muscular strength gains. Results, however, are mixed regarding changes in firing rates in studies that utilize single motor unit recordings. The lack of clarity could be related to vast or subtle differences in RET programs, methods to record motor units, muscles tested, types of contractions and intensities used to record motor units, etc. Yet to be discussed, mixed findings could be the result of non-uniform MU behavior that is not typically accounted for in RET research. The purpose of this narration is to discuss the effects of acute resistance exercise training studies on MU behavior and to provide guidance for future research.
