BIOMECHANICAL AND REFLEX RESPONSES TO JOINT PERTURBATIONS DURING ELECTRICAL-STIMULATION OF MUSCLE - INSTRUMENTATION AND MEASUREMENT TECHNIQUES

A test device is developed to measure ankle joint compliance and muscl e activity when the ankle is subjected to perturbations in angular pos ition (or torque) from bias positions achieved volitionally or via ele ctrical stimulation. The ankle measurement system uses a pivoting foot plate and is operable with the subject sitting or supine. A companion platform for the knee is developed that uses a rotary arm and attached leg brace and is operable with the subject's leg in the horizontal or vertical plane. The knee fixture's pivoting arm can slide to account for the cam-like movement of the knee during rotation. The devices use similar hardware and share common instrumentation and control. Precis e torque or position perturbations are delivered by a computer-control led torque motor to the ankle or knee. Angular displacement, torque, a cceleration, knee fixture moment arm and electromyographic data are co llected on analogue tape and simultaneously digitised and stored. A sp ecial stimulator/recording amplifier permits the recording of electrom yographic signals from the stimulated muscle. Experimental data indica te that the ankle and knee devices, operated horizontally, are purely inertial systems. Sample ankle and knee joint responses to perturbatio ns are presented.