Muscle phenotype is related to motor unit behavior of the vastus lateralis during maximal isometric contractions

Muscle phenotype is related to motor unit behavior of the vastus lateralis during maximal... Previous investigations have reported a relationship between skeletal muscle phenotype and motor unit (MU) firing parameters during submaximal contractions. The purpose of the current investigation, however, was to examine the relationships between motor unit firing behavior during a maximal voluntary contraction, Myosin Heavy Chain (MHC) isoform content, and various molecular neuromuscular targets of the vastus lateralis (VL) muscle in resistance‐trained men. Ten resistance‐trained males completed a trapezoidal ramp contraction up to 100% of their maximal voluntary isometric strength (MVIC). Surface electromyography was recorded from the VL using a multichannel electrode array and decomposed to examine the firing characteristics of individual MUs. A skeletal muscle biopsy of the VL was also collected from each subject. Regression analyses were performed to identify relationships between type II fiber area and the slopes and/or intercepts of the mean firing rate (FRMEAN) versus recruitment threshold (RT), max firing rate (FRMAX) versus RT, and RT versus MU action potential amplitude (MUAPPP) relationships. There were significant inverse relationships between type II fiber area and the y‐intercept of the FR versus RT relationship (P < 0.05). Additionally, strong relationships (r > 0.5) were found between type II fiber area and FRMEAN versus RT slope and RT versus MUAPPP slope and intercept. These data further support the hypothesis that skeletal muscle phenotype is related to MU behavior during isometric contraction. However, our data, in concert with previous investigations, may suggest that these relationships are influenced by the intensity of the contraction. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physiological Reports Wiley

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Publisher
Wiley Subscription Services, Inc., A Wiley Company
Copyright
© 2018 Published by the American Physiological Society and The Physiological Society
ISSN
2051-817X
eISSN
2051-817X
D.O.I.
10.14814/phy2.13636
Publisher site
See Article on Publisher Site

Abstract

Previous investigations have reported a relationship between skeletal muscle phenotype and motor unit (MU) firing parameters during submaximal contractions. The purpose of the current investigation, however, was to examine the relationships between motor unit firing behavior during a maximal voluntary contraction, Myosin Heavy Chain (MHC) isoform content, and various molecular neuromuscular targets of the vastus lateralis (VL) muscle in resistance‐trained men. Ten resistance‐trained males completed a trapezoidal ramp contraction up to 100% of their maximal voluntary isometric strength (MVIC). Surface electromyography was recorded from the VL using a multichannel electrode array and decomposed to examine the firing characteristics of individual MUs. A skeletal muscle biopsy of the VL was also collected from each subject. Regression analyses were performed to identify relationships between type II fiber area and the slopes and/or intercepts of the mean firing rate (FRMEAN) versus recruitment threshold (RT), max firing rate (FRMAX) versus RT, and RT versus MU action potential amplitude (MUAPPP) relationships. There were significant inverse relationships between type II fiber area and the y‐intercept of the FR versus RT relationship (P < 0.05). Additionally, strong relationships (r > 0.5) were found between type II fiber area and FRMEAN versus RT slope and RT versus MUAPPP slope and intercept. These data further support the hypothesis that skeletal muscle phenotype is related to MU behavior during isometric contraction. However, our data, in concert with previous investigations, may suggest that these relationships are influenced by the intensity of the contraction.

Journal

Physiological ReportsWiley

Published: Jan 1, 2018

Keywords: ; ;

References

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