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A system has been developed which is able to impose a fast ankle rotation during gait. The two-link system consists of a mechanical joint which is strapped to the calf and the foot of the subject. The mechanical joint turns around the ankle joint by means of Bowden wires and it is connected to a motor placed next to a treadmill where the subject is walking. By position feedback from the mechanical joint the motor is regulated in such a may that it follows the movement of the ankle joint without influencing the gait pattern. The system is designed to impose a fast ankle rotation with a displacement of up to 20/spl deg/, e.g., a 8/spl deg/ stretch is performed with a rise time of 32 ms during any time of the gait cycle. The system attached to the subject's leg weights in total 0.9 kg. The system is designed to elicit a stretch reflex in the ankle extensor muscles during walking. The prospect of the system is to investigate electrophysiological and biomechanical features during a naturally evoked stretch reflex of the ankle extensors in both healthy and motor impaired subjects. The system is able to produce a perturbation of the ankle extensors at a walking speed of up to 6 km/h during the total gait cycle.
Andersen et al. (Sun,) studied this question.