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Sex‐related differences in muscle size explained by amplitudes of higher‐threshold motor unit action potentials and muscle fibre typing
Author(s) -
Trevino M. A.,
Sterczala A. J.,
Miller J. D.,
Wray M. E.,
Dimmick H. L.,
Ciccone A. B.,
Weir J. P.,
Gallagher P. M.,
Fry A. C.,
Herda T. J.
Publication year - 2019
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/apha.13151
Subject(s) - isometric exercise , motor unit , myosin , major histocompatibility complex , medicine , mathematics , anatomy , endocrinology , biology , genetics , biophysics , antigen
Abstract Aim To investigate the relationships between motor unit action potential amplitudes (MUAP AMP ), muscle cross‐sectional area (mCSA) and composition (mEI), per cent myosin heavy chain (%MHC) areas and sex in the vastus lateralis (VL). Methods Ten males and 10 females performed a submaximal isometric trapezoid muscle action that included a linearly increasing, steady torque at 40% maximal voluntary contraction, and linearly decreasing segments. Surface electromyographic decomposition techniques were utilized to determine MUAP AMPS in relation to recruitment thresholds (RT). Ultrasound images were taken to quantify muscle mCSA and mEI. Muscle biopsies were collected to calculate %MHC areas. Y‐intercepts and slopes were calculated for the MUAP AMP vs RT relationships for each subject. Independent‐samples t tests and ANOVA models examined sex‐related differences in mCSA, mEI, slopes and y‐intercepts for the MUAP AMP vs RT relationships and %MHC areas. Correlations were performed among type IIA and total type II %MHC area, mCSA and the slopes and y‐intercepts for the MUAP AMP vs RT relationships. Results Males exhibited greater slopes for the MUAP AMP vs RT relationships ( P = .003), mCSA ( P < .001) and type IIA %MHC ( P = .011), whereas females had greater type I %MHC area ( P = .010) and mEI ( P = .024). The mCSA, type IIA and total II %MHC area variables were correlated ( P < .001‐.015, r = .596‐.836) with the slopes from the MUAP AMP vs RT relationships. Conclusion Sex‐related differences in mCSA and MUAP AMPS of the higher‐threshold MUs were likely the result of larger muscle fibres expressing type II characteristics for males.