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J Physiol Volume 581, Number 1, 99-105, May 15, 2007 DOI: 10.1113/jphysiol.2007.130088
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RAPID REPORT

Positive force feedback in human walking

 Michael J. Grey1,2,3, Jens Bo Nielsen2,3, Nazarena Mazzaro1 and Thomas Sinkjær1

1 Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark
2 Institute of Exercise and Sport Sciences
3 Department of Medical Physiology, University of Copenhagen, Copenhagen, Denmark

The objective of this study was to determine if load receptors contribute to the afferent-mediated enhancement of ankle extensor muscle activity during the late stance phase of the step cycle. Plantar flexion perturbations were presented in late stance while able-bodied human subjects walked on a treadmill that was declined by 4%, inclined by 4% or held level. The plantar flexion perturbation produced a transient, but marked, presumably spinally mediated decrease in soleus EMG that varied directly with the treadmill inclination. Similarly, the magnitude of the control step soleus EMG and Achilles' tendon force also varied directly with the treadmill inclination. In contrast, the ankle angular displacement and velocity were inversely related to the treadmill inclination. These results suggest that Golgi tendon organ feedback, via the group Ib pathway, is reduced when the muscle–tendon complex is unloaded by a rapid plantar flexion perturbation in late stance phase. The changes in the unload response with treadmill inclination suggest that the late stance phase soleus activity may be enhanced by force feedback.

(Received 2 February 2007; accepted after revision 1 March 2007; first published online 1 March 2007)
Corresponding author M. J. Grey: Institute of Exercise and Sport Sciences & Department of Medical Physiology, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen, Denmark. Email: mgrey{at}mfi.ku.dk






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