The effects of speed variation on joint kinematics during multisegment reaching movements

This study examined the effects of speed variation on the joint kinematic c haracteristics during multisegment reaching movements. An experiment was co nducted in which six subjects performed a wide variety of seated reaching m ovements using two speed modes within a volitional range. Motions of the up per torso and right arm were measured by tracking markers on surface body l andmarks using a four-camera opto-electronic movement analysis system. Join t angle profiles were derived from the measured locations of surface marker s, based on a 7-DOF biomechanical linkage model. These angle profiles were then mathematically characterized by four-parameter hyperbolic tangent func tions through a non-linear curve fitting process. Accurate characterization of the profiles (mean R-2 = 0.99) allowed subsequent statistical analysis including both multi- and uni-variate ANOVA to test the speed effects on th e parameters collectively as well as individually. The study revealed the f ollowing: (I)neither the joint angle selection nor the amplitude of the sel ected 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 (r ime-scaled) for the primary descending/ascending but a greater fraction of total time for accelerating phase where the velocity and acceleration are i n the same direction. (C) 1999 Elsevier Science B.V. All rights reserved.