We have investigated whether differences in EMG activity in mono- and bi-articuiar muscles for concentric and eccentric contractions (van Bolhuis, Gielen, & van Ingen Schenau, 1998) have to be attributed to a specific muscle coordination strategy or whether they are merely a demonstration of adaptations necessary to adjust for muscle contractile properties. Slow, multi-joint arm movements were studied in a horizontal plane with an external force applied at the wrist. Kinematics and electromyography data from 10 subjects were combined with data from a 3-D model of the arm and a Hill-type muscle model Data for both mono- and bi-articular muscles revealed a higher activation in concentric than in eccentric contractions. The model calculations indicated that the measured difference in activation (20%) was much larger than expected based on the force-velocity relationship (predicting changes of ~5%). Although these findings eliminate the force-velocity relationship as the main explanation for changes in EMG, it cannot be ruled out that other muscle contractile properties, such as history dependence of muscle force, determine muscle activation levels in the task that was studied.
T.G. Welter, M.F. Bobbert, L.A. Rozendaal, and D.H.E.J. Veeger are with the Institute for Fundamental and Clinical Human Movement Sciences at the Vrije Universiteit Amsterdam, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands. B.M. Van Bolhuis and C.C.A.M. Gielen are with the Department of Medical Biophysics at the University of Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands.