Proprioceptive modulation of hip flexor activity during the swing phase oflocomotion in decerebrate cats

This study examined the influence of proprioceptive input from hip flexor m uscles on the activity in hip flexors during the swing phase of walking in the decerebrate cat. One hindlimb was partially denervated to remove cutane ous input and afferent input from most other hindlimb muscles. Perturbation s to hip movement were applied either by 1) manual resistance or assistance to swing or by 2) resistance to hip flexion using a device that blocked hi p flexion but allowed leg extension. Electromyographic recordings were made from the iliopsoas (IP), sartorius, and medial gastrocnemius muscles. When the hip was manually assisted into flexion, there was a reduction in hip f lexor burst activity. Conversely, when hip flexion was manually resisted or mechanically blocked during swing, the duration and amplitude of hip flexo r activity was increased. We also found some specificity in the role of aff erents from individual hip flexor muscles in the modulation of flexor burst activity. If the IP muscle was detached from its insertion, little change in the response to blocking flexion was observed. Specific activation of IP afferent fibers by stretching the muscle also did not greatly affect flexo r activity. On the other hand, if conduction in the sartorius nerves was bl ocked, there was a diminished response to blocking hip flexion. The increas e in duration of the flexor bursts still occurred, but this increase was co nsistently lower than that observed when the sartorius nerves were intact. From these results we propose that during swing, feedback from hip flexor m uscle afferents, particularly those from the sartorius muscles, enhances fl exor activity. In addition, if we delayed the onset of flexor activity in t he contralateral hindlimb, blocking hip flexion often resulted in the prolo ngation of ipsilateral flexor activity for long, periods of time, further r evealing the reinforcing effects of flexor afferent feedback on flexor acti vity. This effect was not seen if conduction in the sartorius nerves was bl ocked. In conclusion, we have found that hip flexor activity during locomot ion can be strongly modulated by modifying proprioceptive feedback from the hip flexor muscles.