Abstract

This study examined the effects of speed variation on the joint kinematic characteristics during multisegment reaching movements. An experiment was conducted in which six subjects performed a wide variety of seated reaching movements using two speed modes within a volitional range. Motions of the upper torso and right arm were measured by tracking markers on surface body landmarks using a four-camera opto-electronic movement analysis system. Joint angle profiles were derived from the measured locations of surface markers, based on a 7-DOF biomechanical linkage model. These angle profiles were then mathematically characterized by four-parameter hyperbolic tangent functions through a non-linear curve fitting process. Accurate characterization of the profiles (mean R2 = 0.99) allowed subsequent statistical analysis including both multi- and uni-variate ANOVA to test the speed effects on the parameters collectively as well as individually. The study revealed the following: (1) neither the joint angle selection nor the amplitude of the selected angle motions was significantly influenced by the speed variation, (2) neither the time-scaling effect nor the symmetry of velocity profile in a strict sense was present, and (3) a faster speed induced a steeper rate (time-scaled) for the primary descending/ascending but a greater fraction of total time for accelerating phase where the velocity and acceleration are in the same direction. Verf.-Referat