The dynamic response of the human ankle joint to a band-limited (0 to 50 Hz) gaussian torque disturbance superimposed on a constant bias torque is observed at different levels of voluntary contraction of the leg muscles acting about the ankle. The compliance of the ankle joint, defined as the ratio of the joint rotation and applied torque is modeled by a second-order, linear dynamic model. The visco-elastic properties of the joint are shown to be linear functions of the muscle activation.