Use-dependent gain change in the reflex contribution to extensor activity in walking cats

Denervation of the synergists of the medial gastrocnemius (MG) muscle in th e cat hind leg results in a progressive increase in the magnitude of burst activity in the MG muscle during walking. The increase in burst magnitude i s associated with an increase in the slope of the relationship between the magnitude of individual MG bursts and the amplitude of ankle flexion during stance. This finding is consistent with the hypothesis that the increase i n MG burst magnitude is due to an increase in gain of reflex pathways reinf orcing the activation of MG. The increase in slope is use-dependent since i t was not observed when the leg was released from a cast that immobilized t he leg for 6 days. (C) 2000 Elsevier Science B.V. All rights reserved.