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The hypothesis that strength of active muscles affects the symmetry of the velocity profiles of voluntary movements was tested. In particular, it was assumed that the duration of acceleration and deceleration phases reflects the ability of the antagonistic muscles to exert torque in such a way that stronger muscle requires less time for action. Twelve subjects performed consecutive 50° flexions and extensions in blocks of either discrete or oscillatory movements. They were tested under high and moderate speed conditions, as well as within different ranges of elbow joint angles. The symmetry ratio (SR; acceleration lime divided by deceleration time) was calculated in order to assess movement symmetry. The results demonstrated SR > 1 under most of the discrete and, particularly, oscillatory movement conditions. A velocity-associated increase in SR was recorded, while different ranges of elbow movements, assumed to provide different torques of the agonist and antagonist muscles, also provided different SR. The findings were generally in line with the predicted effects of movement conditions on muscle strength, particularly those related to elbow angle and elbow angular velocity. Deviations from me ideal movement symmetricity have usually been interpreted as either weakness of various motor control models and hypotheses, or as a sub-optimal control of movements in certain subject populations; the present study suggests an alternative interpretation based upon the ability of active muscles to exert torque.
D.M. Mirkov is with the Department of Biophysics in me School of Medicine at Belgrade University, 11 000 Belgrade. Yugoslavia. S. Milanovic is with the Institute for Medical Research, Box 102, 11 129. Belgrade, Yugoslavia. D.B. Ilic is with the Research Center in the Faculty for Sports and Physical Education at Belgrade University. S. Jaric is with the Centre for Musculo skeletal Research at Umea University and the National Institute for Working Life. Box 7654, S-907 13 Umea. Sweden.