Fatigue affects the capacity of muscles to generate forces and is associated with characteristic changes in EMG signals. It may also influence interjoint and intermuscular coordination. To understand better the global effects of fatigue on multijoint movement, we studied movement kinematics and EMG changes in healthy volunteers asked to hammer repetitively. Movement kinematics and the activity of 20 muscles of the arm, trunk, and leg were recorded before and after subjects became fatigued (as measured using a Borg scale). When fatigue was reached, maximal grip strength and elbow range of motion decreased while the EMG amplitude of the contralateral external oblique muscle was increased. Fatigue did not affect shoulder and wrist kinematics or movement frequency. Results suggest that fatigue influences motion at both local and global levels. Specifically, interjoint and intermuscular coordination adapt to compensate for local effects of fatigue and to maintain key movement characteristics, such as the trajectory of the end effector and the movement frequency. Nonlocal compensations may be a focus of future studies of how fatigue affects complex movements such as those typically performed in the workplace.
Côté, Feldman, and Levin are with the Jewish Rehabilitation Hospital, Center for Interdisciplinary Research in Rehabilitation of Montreal (CRIR), Quebec, Canada H3S 2J4. Côté and Levin are also with McGill University, Montreal, Quebec, Canada H2W 1S4. Feldman and Mathieu are with the Institute of Biomedical Engineering, University of Montreal, Quebec, Canada H3T 1J4.