![]() ![]() The constant latency of the stretch reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. During the stance phase the maximal EMG stretch reflex had a phase lead of approximately 120 ms with respect to the maximal background EMG and a phase lead of approximately 250 ms with respect to the maximal nonreflex torque. At heel contact the nonreflex torque was 50% of its maximal value. The torque measured over the first 35 ms after stretch onset (nonreflex torque) was at a maximum during late stance, when the leg supported a large part of the body's weight, and at a minimum during the swing phase. When the ankle joint is rotated, a change in torque can be measured. The onset (42 +/- 3.2 ms) and peak latencies (59 +/- 2.5 ms) of the stretch reflex did not depend on the phase in the step cycle at which the reflex was elicited. In late swing, the stretch reflex amplitude increased to 45 +/- 27% (mean +/- SD) of the maximal amplitude in the stance phase (stretch amplitude 8 degrees, stretch velocity 250 degrees/s). In the transition from stance to swing, the amplitude was 0 in all subjects. In the stance phase, the amplitude equaled that found during standing at matched soleus background electromyogram (EMG). ![]() The short-latency soleus stretch reflex was modulated during a step. The weight of the total system attached to the leg of the subject was 900 g. The system consisted of a mechanical joint attached to the subject's ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. Ankle joint stretches were applied by a system able to rotate the human ankle joint during treadmill walking in any phase of the step cycle. The modulation of the short-latency stretch reflex during walking at different walking speeds was investigated and compared with the stretch reflex during standing in healthy human subjects. ![]()
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