title: Inter-individual variability in the torque-related patterns of responses for mechanomyographic amplitude and mean power frequency.
abstract: The purpose of this study was to examine the inter-individual variability for the patterns of responses for mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus isometric torque in lower-strength (LS) and higher-strength (HS) individuals. Twelve participants (mean +/- S.D. age = 25 + 4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing nine submaximal step muscle actions (15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% MVC) of the right leg extensors. MMG signals were recorded from the vastus lateralis muscle, and MMG amplitude and MPF values were computed for each corresponding percentage of the MVC. Polynomial regression analyses indicated that the composite MMG amplitude versus isometric torque relationship was best fit with a linear model (r(2) = 0.980) for the LS group and a cubic model (r(2) = 0.994) for the HS group. The composite MMG MPF versus isometric torque relationships were best fit with linear models for both the LS (r(2) = 0.529) and HS (r(2)=0.591) groups. However, only 66% of the individuals exhibited the same linear MMG amplitude patterns as the composite relationship for the LS group, whereas only 33% of the individual relationships were cubic for the HS group. Only one subject exhibited a positive linear (r(2) = 0.681) relationship for the MMG(MPF) versus isometric torque relationship for either the LS or HS groups. These findings suggested that strength differences do not affect the patterns of responses for MMG amplitude or MPF. The lack of consistency between the individual and composite patterns of responses suggested some degree of inter-individual variability. Therefore, future studies should examine the individual patterns of response to draw conclusions about motor control strategies.
authors.affiliation: Department of Health and Exercise Science, Biophysics Laboratory, University of Oklahoma, 1401 Asp Avenue, Norman, OK 73019-6081, USA. eryan@ou.edu
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ryan
authors.forename: Joel T
authors.initials: JT
authors.lastname: Cramer
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Housh
authors.forename: Travis W
authors.initials: TW
authors.lastname: Beck
authors.forename: Trent J
authors.initials: TJ
authors.lastname: Herda
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hartman
mesh_terms: D000054:Acceleration; D001696:Biomechanical Phenomena / Q000379:methods*; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009213:Myography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019415:Torque