Mechanomyographic and electromyographic amplitude and frequency responses from the superficial quadriceps femoris muscles during maximal, eccentric isokinetic muscle actions

The purposes of this study were to examine the effects of gender and muscle (vastus lateralis = VL, rectus femoris = RF, and vastus medialis = VM) on the velocity-related patterns for peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, MMG mean power frequency (MPF), and EMG MPF during maximal, eccentric isokinetic muscle actions. Thirteen females (mean ± SD age = 21 ± 1 years) and eleven males (mean ± SD age = 21 ± 2 years) volunteered for this investigation. PT and MP were measured on a calibrated Cybex 6000 dynamometer at randomly ordered velocities of 60, 120, and 180°.s^-1, while MMG and EMG signals were recorded simultaneously from the VL, RF, and VM muscles. The results indicated no gender-related differences for the patterns of PT, MP, MMG amplitude, EMG amplitude, MMG MPF, or EMG MPF. Furthermore, no muscle-related differences were found for the patterns of MMG amplitude, EMG amplitude, or MMG MPF. The normalized values for MP and MMG amplitude increased from 60 to 180°.s^-1 (60°.s^-1 < 120°.s^-1 < 180°.s^-1). PT and EMG MPF remained unchanged across velocity, while EMG amplitude remained unchanged from 60 to 120°.s^-1, but decreased (approximately 10%) from 120 to 180°.s^-1. The findings indicated a close association between the patterns for MP and MMG amplitude, and a similarity between the patterns for PT, EMG amplitude, and EMG MPF across velocity. Therefore, the present findings suggested that motor unit recruitment (EMG amplitude), firing rate (MMG MPF), and muscle fiber action potential conduction velocity (EMG MPF) exhibited velocity-related patterns that were similar to PT production, while MMG amplitude was more closely associated with MP.