A bilateral electro-hydraulic actuator system to measure dynamic ankle joint stiffness during upright human stance

The role of the stretch reflex during upright stance remains unclear despite research that has been conducted to date. We have developed a bilateral electro-hydraulic actuator system to measure the dynamic joint stiffness of the human ankle during standing and help understand the role of the stretch reflex in the control of posture. The apparatus consists of two foot pedals that are each connected to an electro-hydraulic rotary actuator. Transducers were incorporated to measure the position and torque of each actuator, the angle of the ankle with respect to the foot plate, and the positions of the knee and hip. The experimental apparatus allows independent perturbations to be applied to each ankle. One subject was studied using the new apparatus and the results showed that reflexes are present during the perturbed standing task.