Electromyographic and mechanomyographic responses across repeated maximal isometric and concentric muscle actions of the leg extensors

The purpose of the present study was to examine the patterns of responses for torque, electromyographic (EMG) amplitude, EMG mean power frequency (MPF), mechanomyographic (MMG) amplitude, and MMG MPF across 30 repeated maximal isometric (ISO) and concentric (CON) muscle actions of the leg extensors. Twelve female subjects (21.1 ± 1.4 yrs; 63.3 ± 7.4 kg) performed ISO and CON fatigue protocols with EMG and MMG signals recorded from the vastus lateralis. The relationships for torque, EMG amplitude, EMG MPF, MMG amplitude, and MMG MPF versus repetition number were examined using polynomial regression. The results indicated there were decreases (p < 0.05) across the ISO muscle actions for torque (r2 = 0.95), EMG amplitude (R2 = 0.44), EMG MPF (r2 = 0.62), and MMG MPF (r2 = 0.48), but no change in MMG amplitude (r2 = 0.07). In addition, there were decreases across the CON muscle actions for torque (R2 = 0.97), EMG amplitude (R2 = 0.46), EMG MPF (R2 = 0.86), MMG amplitude (R2 = 0.44), and MMG MPF (R2 = 0.80). Thus, the current findings suggested that the mechanisms of fatigue and motor control strategies used to modulate torque production were similar between maximal ISO and CON muscle actions.