Soleus stretch reflex Modulation during gait in man. Sinkj_r, ®MDNM¯Thomas, Jacob B. Andersen, Birgit Larsen. Center for Sensory-Motor Interaction, Department of Medical Informatics and Image Analysis, Aalborg University, Fredrik Bajers Vej 7D, DK-9220 Aalborg, Denmark.
APStracts 3:0053N, 1996.
1. The modulation of the short latency stretch reflex during walking at different walking speeds was investigated and compared to the stretch reflex during standing in healthy human subjects. 2. 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 system consisted of a mechanical joint attached to the subjects ankle joint and connected to a motor placed beside the treadmill by means of bowden wires. The weight of the total system attached to the leg of the subject was 900 g. 3. The short latency soleus stretch reflex was modulated during a step. In the stance phase the amplitude equalled the one found during standing at matched soleus background EMG. In the transition from stance to swing the amplitude was zero in all subjects. In late swing the stretch reflex amplitude increased to 45 + 27% (mean + 1 S.D.) of the maximal amplitude in the stance phase (stretch amplitude 8 o , stretch velocity 250 o /s). 4. 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 where it was elicited. 5. When the ankle joint is rotated, a change in torque can be measured. The torque measured over the first 35 ms after stretch onset (non- reflex 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. At heel contact the non-reflex torque was 50% of its maximal value. 6. 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 non-reflex torque. 7. The constant latency of the stretch reflex during a step implied that the ankle extensor muscle spindles are always taut during walking. 8. The relatively high amplitude of the stretch reflex in late swing and at heel contact made it likely that the stretch reflex contributed to the activation of the ankle extensor muscles in early stance phase.

Received 8 September 1995; accepted in final form 8 March 1996.
APS Manuscript Number J601-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96