Nonlinearities 1 Running Head: NONLINEARITIES IN HAND AND FOOT COORDINATION Nonlinearities in Hand and Foot Coordination

Biomechanical studies performed over the past thirty years have demonstrated that the simultaneous motion of human appendages exhibits significant coordination or “synergy” and that this dependence of the motion of seemingly independent body extremities is highly nonlinear. The present paper reports new experimental research conducted with a group of subjects for the case of coupled hand and foot movements. In these experiments, a series of discrete synchronized hand-foot movement trials are performed. Subjects attempt to move one hand and one foot simultaneously from a start to target location (horizontal translation), while simultaneously moving one of these appendages (hand or foot) vertically to clear a barrier. In the experiments, the effects of right-left limb pairing, direction of movement in relation to the body and the placement of a path-obstructing barrier are investigated. To quantitatively study the phenomenon, data consisting of time histories of the moving limbs are digitally recorded, processed with a data reduction program and statistically analyzed. Results show that the effect of foot motion on the motion of the hand is greater than the corresponding effect of hand motion on the foot. Another nonlinearity is revealed in examining the velocity of these coordinated motions; i.e. the hand is observed to move with greater initial velocity than the foot, irrespective of whether it is clearing the obstacle or mimicking. This curious phenomenon is discussed in the paper together with the results of analysis of the other measured data.