Force and EMG power spectrum in response to concentric and eccentric exercise

Twenty males performed three bouts of 32 unilateral concentric (CON) or eccentric (ECC) quadriceps muscle actions (180°/s^-1 ). Surface electromyography (EMG) and torque were recorded from the m. vastus lateralis and m. rectus femoris. Mean power frequency (MPF) of the EMG and torque were calculated for seven blocks of four consecutive muscle actions. Torque was greater for ECC than for CON muscle actions. It decreased almost linearly for each CON bout, but remained unchanged for ECC. MPF decreased in each CON bout and only a partial recovery was noticed between bouts. In contrast, MPF was unchanged for a single bout or across bouts of ECC exercise. Thus, changes typically associated with a MPF shift are small or nonexistent during ECC but not during CON exercise