MECHANOMYOGRAPHIC AND ELECTROMYOGRAPHIC RESPONSES OF THE SUPERFICIAL QUADRICEP FEMORIS MUSCLES DURING FATIGUING, CONCENTRIC, ISOKINETIC MUSCLE ACTIONS

Abstract

The purpose of this investigation was to examine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadricep muscles during fatiguing isokinetic muscle actions of the dominant leg extensors. Ten adults (age 21 ± 3 years) volunteered to perform 50 consecutive, maximal concentric muscle actions using a calibrated Cybex 6000 dynamometer at a contraction velocity of 180°s−1. Bipolar surface electrode arrangements were placed over the longitudinal axes of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). An MMG sensor was placed between the EMG electrodes on each muscle. The EMG and MMG amplitude values (root mean square, rms) were calculated for the muscle action producing the highest torque and every five muscle actions beginning with the fifth and ending with the fiftieth. The MMG and EMG amplitude values, and torque were normalized to each respective maximal value then averaged across all subjects. Polynomial regression analyses indicated that torque decreased (p < 0.05) quadratically across the 50 muscle actions, while MMG amplitude decreased linearly for the VL and RF, but quadratically for the VM. EMG amplitude decreased linearly for the VL and VM, and remained unchanged for the RF. These findings indicated that there were differences between the superficial quadriceps muscles in MMG and EMG responses to fatiguing, dynamic muscle actions.