Force and EMG power spectrum during eccentric and concentric actions

INTRODUCTION: This study was designed to examine the force and activation levels of elbow flexor muscles during preactivated eccentric, concentric and isometric actions. METHODS: Force, average EMG (aEMG), and the EMG power spectrum were investigated at different constant movement velocities (1 rad x s(-1), 2 rad x s(-1), 3 rad x s(-1), and 4 rad x s(-1)) at different joint angles. RESULTS: Average force at a 110 degree elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric actions. At a 55 degree elbow angle, there was no difference in aEMG, or it was slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastest velocities at the 110 degree elbow angle, whereas no difference was observed at the 55 degree elbow angle. In concentric action, MF was higher in 4 rad x s(-1) in comparison with 1 rads x s(-1) at 110 degree elbow angle. DISCUSSION: These results suggest that it is difficult to maintain the maximal eccentric force throughout the whole range of motion. Maximal EMG activity and frequencies of the EMG power spectrum can be at the same level or lower in eccentric actions as compared with concentric actions, depending on the joint angle and preactivation mode. The results of the EMG power spectrum do not support the concept that in maximal eccentric actions fast units are selectively activated.