Time Course of Changes in Neuromuscular Parameters from the Quadriceps During Maximal Isokinetic Muscle Actions

Cory M. Smith, Terry J. Housh, Ethan C. Hill, Joshua L. Keller, Glen O. Johnson, Richard J. Schmidt

Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA


Purpose: The purposes of the present study were to identify the time course of changes in neuromuscular responses and to infer about the motor unit control strategies used to maintain force from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) during a fatiguing maximal concentric isokinetic leg extension workbout.

Methods: Thirteen men performed 25 maximal concentric isokinetic leg extension muscle actions at 120°s-1. Electromyography, (EMG), mechanomyography (MMG), and force were simultaneously collected from the VL, VM, and RF during each of the 25 repetitions. A combined regression and mean comparisons analysis was used to examine the time course of changes in maximal isokinetic peak force as well as EMG amplitude (RMS), EMG mean power frequency (MPF), MMG RMS, and MMG MPF from the VL, VM, and RF.

Results: Maximal isokinetic peak force decreased 21% and was accompanied by changes in neuromuscular responses from all muscles. The VL exhibited increases in EMG RMS and MMG RMS, decreases in EMG MPF, but no changes in MMG MPF. The VM only exhibited increases in EMG RMS. The RF, however, exhibited increases in EMG RMS, but decreases in EMG MPF.

Discussion: The time course of changes in neuromuscular responses allowed for the identification of the potential motor unit control strategies used to maintain and optimize force production. The motor unit control strategy utilized to maintain and optimize force production could not be explained by the After-Hyperpolarization or Muscle Wisdom theory, but could be explained by the Onion Skin Scheme. Journal of Nature and Science (JNSCI), 3(8):e426, 2017



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