Compensation for substrate elasticity in the kinematics of leaping by infant pigtailed macaques (Macaca nemestrina).

The means whereby animals adapt their locomotor behavior to variation in environmental conditions is an important and neglected problem in the area of motor control. To investigate this problem, young (3-month-old) pigtailed macaques (Macaca nemestrina) were filmed leaping a fixed distance from both rigid and elastic take-off supports. Sixteen of 17 subjects exhibited substantial invariance in the trajectories described by the major joints of the hind limb (hip, knee and ankle) during the leap. By contrast, the patterns of angular joint movement varied between performances involving the rigid and elastic supports. Maintaining invariant joint trajectories may enable the leaping animal to land safely at the target and prepare for subsequent action, and requires compensation for substrate elasticity. This compensation is effected, in part, by changing the patterns of joint flexion and extension.