Mechanomyographic and electromyographic responses of the superficial muscles of the quadriceps femoris during maximal, concentric isokinetic muscle actions

Eleven adult males (mean ± SD age = 22 ± 3 years) performed maximal, concentric isokinetic leg extension muscle actions at velocities of 60, 120, 180, 240, and 300°·s^-1 on a Cybex 6000 dynamometer. The results indicated that peak torque (PT) decreased (p < 0.05) as muscle action velocity increased. Mechanomyographic (MMG) amplitude increased with velocity to 180°·s(-l) for each muscle tested (vastus lateralis = VL, rectus femoris = RF, and vastus medialis = VM). For the VL, MMG amplitude continued to increase to 240°·s(-l) and then plateaued, while the RF plateaued from 180 to 300°·s^-1. The VM showed a constant increase in MMG amplitude to 300°·s^-1. Electromyographic (EMG) amplitude increased to 180°·s^-1 and then plateaued for each muscle. These findings indicated muscle-specific differences in MMG amplitude patterns across velocity that may be attributable to differences in fiber type composition, muscle architecture, and/or tissue layer composition. Furthermore, these results suggested that there were muscle-specific, velocity-related differences in the association between motor unit activation (EMG) and the mechanical aspects of muscular activity (MMG).