Force and EMG power spectrum during eccentric and concentric actions

Introduction: This study was designed to examine the force and activation l evers of elbow flexor muscles during preactivated eccentric, concentric and isometric actions. Methods: Force, average EMG (aEMG), and the EMG power s pectrum were investigated at different constant movement velocities (1 rad. s(-1), 2 rad.s(-1), 3 rad.s(-1), and 4 rad.s(-1)) at different joint angles . Results: Average force ata 110 degrees elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric acti ons. At a 55 degrees elbow angle, there was no difference in aEMG, or it wa s slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastest velocities at the 110 degrees elbow angle, whereas no difference was observed at the 55 degrees e lbow angle. In concentric action, MF was higher in 4 rad.s(-1) in compariso n with 1 rad.s(-1) at 110 degrees elbow angle. Discussion: These results su ggest that it is difficult to maintain the maximal eccentric force througho ut the whole range of motion. Maximal EMG activity and frequencies of the E MG power spectrum can be at the same level or lower in eccentric actions as compared with concentric actions, depending on the joint angle and preacti vation mode. The results of the EMG power spectrum do not support the conce pt that in maximal eccentric actions East units are selectively activated.