Mechanomyographic and Electromyographic Responses to Repeated, Concentric Muscle Actions

Abstract

0815 PURPOSE: The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) responses of the superficial quadricep femoris muscles during repeated, concentric muscle actions of the dominant leg. METHODS: Fifteen adults (21.8 ± 1.7 yrs) performed 50 consecutive, maximal concentric muscle actions on a Biodex System 3 Dynamometer at a velocity of 60°×s−1. Bipolar surface electrode arrangements were placed over the mid portion of the vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) muscles with a MMG contact sensor placed adjacent to the superior EMG electrode on each muscle. Torque, power, and MMG and EMG amplitude and MPF values were calculated for each of the 50 repetitions. All values were normalized to the value recorded during the first repetition and then averaged across all subjects. RESULTS: Polynomial regression analysis indicated cubic decreases in torque (R2 = 0.976) and power (R2 = 0.973) across all 50 muscle actions. EMG amplitude increased quadratically for the VL (R2 = 0.362) and cubically for the RF (R2 = 0.528) and VM (R2 = 0.419). EMG MPF decreased across muscle actions with a quadratic relationship for the VL (R2 = 0.865) and VM (R2 = 0.821) and a cubic relationship for the RF (R2 = 0.979). MMG amplitude decreased cubically for the VL (R2 = 0.316) and RF (R2 = 0.563), but there was no change in the MPF for the VM (R2 = 0.043). MMG MPF decreased quadratically for the VL (R2 = 0.601) and linearly for the RF (R2 = 0.788) and VM (R2 = 0.457). CONCLUSION: These findings indicate muscle-specific dissociations between EMG and MMG amplitude across the 50 repetitions where EMG amplitude increased and MMG amplitude decreased. The decrease in MMG amplitude and MPF may be due to a decrease in motor unit discharge rates associated with “muscle wisdom”. Further, these results suggest that “muscle wisdom” may be muscle specific. Future studies should examine the applicability of muscle wisdom during dynamic muscle actions.