Open AccessMuscle phenotype is related to motor unit behavior of the vastus lateralis during maximal isometric contractions
Author(s) -
Colquhoun Ryan J.,
Magrini Mitchel A.,
Haun Cody T.,
Muddle Tyler W. D.,
Tomko Patrick M.,
Luera Micheal J.,
Mackey Cameron S.,
Vann Christopher G.,
Martin Jeffrey S.,
Young Kaelin C.,
DeFreitas Jason M.,
Roberts Michael D.,
Jenkins Nathaniel D. M.
Publication year - 2018
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.13636
Subject(s) - isometric exercise , motor unit , vastus lateralis muscle , electromyography , skeletal muscle , motor unit recruitment , myosin , muscle contraction , medicine , muscle biopsy , contraction (grammar) , cardiology , anatomy , chemistry , physical medicine and rehabilitation , biology , biopsy , biophysics
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 MU s. 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 ( FR MEAN ) versus recruitment threshold ( RT ), max firing rate ( FR MAX ) versus RT , and RT versus MU action potential amplitude ( MUAP PP ) 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 FR MEAN versus RT slope and RT versus MUAP PP 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.