Endurance training alters motor unit activation strategies for the vastus lateralis, yet sex-related differences and relationships with muscle size remain

Sontag, Stephanie A.; Trevino, Michael A.; Herda, Trent J.; Sterczala, Adam J.; Miller, Jonathan D.; Parra, Mandy E.; Dimmick, Hannah L.; Deckert, Jake A.

doi:10.1007/s00421-021-04622-7

Cited by 8 publications

(18 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Despite smaller mCSA for the VL 8,39–41 and lower MVC for the knee extensors 28,41,42 for the females, the slopes and y ‐intercepts for the IFR versus RT relationships were the only sex‐related differences in MU properties for the 40% MVC. However, a low percentage (45%) of the relationships for the females were significant; therefore, the physiological interpretation for the coefficients between males and females is unclear.…”

Section: Discussionmentioning

confidence: 88%

Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

et al. 2023

Self Cite

View full text Add to dashboard Cite

AimsMotor unit recruitment and firing rate patterns of the vastus lateralis (VL) have not been compared between sexes during moderate‐ and high‐intensity contraction intensities. Additionally, the influence of fiber composition on potential sex‐related differences remains unquantified.MethodsEleven males and 11 females performed 40% and 70% maximal voluntary contractions (MVCs). Surface electromyographic (EMG) signals recorded from the VL were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP), initial firing rates (IFRs), mean firing rates (MFRs), and normalized EMG amplitude (N‐EMGRMS) at steady torque were analyzed. Y‐intercepts and slopes were calculated for MUAPAMP, IFR, and MFR versus RT relationships. Type I myosin heavy chain isoform (MHC) was determined with muscle biopsies.ResultsThere were no sex‐related differences in MU characteristics at 40% MVC. At 70% MVC, males exhibited greater slopes (p = 0.002) for the MUAPAMP, whereas females displayed greater slopes (p = 0.001–0.007) for the IFR and MFR versus RT relationships. N‐EMGRMS at 70% MVC was greater for females (p < 0.001). Type I %MHC was greater for females (p = 0.006), and was correlated (p = 0.018–0.031) with the slopes for the MUAPAMP, IFR, and MFR versus RT relationships at 70% MVC (r = −0.599–0.585).ConclusionBoth sexes exhibited an inverse relationship between MU firing rates and recruitment thresholds. However, the sex‐related differences in MU recruitment and firing rate patterns and N‐EMGRMS at 70% MVC were likely due to greater type I% MHC and smaller twitch forces of the higher threshold MUs for the females. Evidence is provided that muscle fiber composition may explain divergent MU behavior between sexes.

show abstract

Section: Discussionmentioning

confidence: 88%

Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

et al. 2023

Self Cite

View full text Add to dashboard Cite

show abstract

“…In contrast, females generally have lower threshold MUs due to the smaller CSA of type II fibres, resulting in lower action potential amplitudes and produce a lower contractile force. Therefore, males rely on lower firing rates to modulate contractile force than females (Trevino et al 2019;Sontag et al 2021). These sex differences in neuromuscular activation are important in explaining the apparent differences in fatigue between males and females.…”

Section: Molecular Differences Between Male and Female Musclementioning

confidence: 99%

“…Whether there are sex differences in neuromuscular adaptations in response to exercise training has not been explored extensively. One study investigated changes in response to 10 weeks of endurance cycling, finding no differences in neuromuscular adaptations between sexes (Sontag et al 2021). To our knowledge, no study has investigated neuromuscular adaptation in response to resistance training between sexes.…”

Section: Molecular Differences Between Male and Female Musclementioning

confidence: 99%

See 1 more Smart Citation

Physiological and molecular sex differences in human skeletal muscle in response to exercise training

Landen

Hiam

Voisin

et al. 2021

The Journal of Physiology

View full text Add to dashboard Cite

Sex differences in exercise physiology, such as substrate metabolism and skeletal muscle fatigability, stem from inherent biological factors, including endogenous hormones and genetics. Studies investigating exercise physiology frequently include only males or do not take sex differences into consideration. Although there is still an underrepresentation of female participants in exercise research, existing studies have identified sex differences in physiological and molecular responses to exercise training. The observed sex differences in exercise physiology are underpinned by the sex chromosome complement, sex hormones and, on a molecular level, the epigenome and transcriptome. Future research in the field should aim to include both sexes, control for menstrual cycle factors, conduct large‐scale and ethnically diverse studies, conduct meta‐analyses to consolidate findings from various studies, leverage unique cohorts (such as post‐menopausal, transgender, and those with sex chromosome abnormalities), as well as integrate tissue and cell‐specific ‐omics data. This knowledge is essential for developing deeper insight into sex‐specific physiological responses to exercise training, thus directing future exercise physiology studies and practical application.

show abstract

“…For example, greater b terms (slopes) calculated from the log-transformed MMG RMS –force/torque relationships during linearly increasing and decreasing muscle actions, and MMG RMS values at steady force/torque, have been reported for individuals expressing greater amounts of type II percent myosin heavy chain isoform content [ 23 , 24 , 25 , 26 ]. In addition, MMG RMS –torque relationships can also be influenced by muscle architecture [ 27 ]. Sontag et al [ 27 ] reported relationships between the muscle cross-sectional area of the vastus lateralis and the b terms (slopes) calculated from the log-transformed MMG RMS –torque relationships during an isometric ramp muscle action up to 70% of maximal strength, such as individuals with larger muscles exhibited b terms that plateaued later (greater slope values) throughout the torque spectrum.…”

Section: Introductionmentioning

confidence: 99%

Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude–Torque Relationships and Sex-Related Differences in the Vastus Lateralis

Trevino

Perez

Sontag

et al. 2023

JFMK

View full text Add to dashboard Cite

This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMGRMS)–torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMGRMS–torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMGRMS was averaged during the plateau. Males exhibited greater PA (p < 0.001), MT (p = 0.027), b terms (p = 0.005), and MMGRMS (p = 0.016). The b terms were strongly (p < 0.001, r = 0.772) and moderately correlated (p = 0.004, r = 0.571) with PA and MT, respectively, while MMGRMS was moderately correlated with PA (p = 0.018, r = 0.500) and MT (p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMGRMS between sexes.

show abstract

Endurance training alters motor unit activation strategies for the vastus lateralis, yet sex-related differences and relationships with muscle size remain

Cited by 8 publications

References 40 publications

Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

Sex‐related differences in motor unit behavior are influenced by myosin heavy chain during high‐ but not moderate‐intensity contractions

Physiological and molecular sex differences in human skeletal muscle in response to exercise training

Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude–Torque Relationships and Sex-Related Differences in the Vastus Lateralis

Contact Info

Product

Resources

About