To investigate the role of localized, proprioceptive feedback in the regulation of interjoint coordination during locomotion, we substantially attenuated neural feedback from the triceps surae muscles in one hindlimb in each of four cats using the method of self-reinnervation. After allowing the recovery of motor innervation, the animals were filmed during level and ramp walking. Deficits were small or undetectable during walking on the level surface or up the ramp, behaviors that require a large range of forces in the triceps surae muscles. During walking down the ramp, when the triceps surae muscles normally undergo active lengthening, the ankle joint underwent a large yield and the coordination between ankle and knee was disrupted. The correlation of the deficit with the direction of length change and not muscle force suggested that a loss of feedback from muscle spindle receptors was primarily responsible for the deficit. These results indicate an important role for the stretch reflex and stiffness regulation during locomotion.

No abstract

In this study, we sought to identify sensory circuitry responsible for motor deficits or compensatory adaptations after peripheral nerve cut and repair. Self-reinnervation of the ankle extensor muscles abolishes the stretch reflex and increases ankle yielding during downslope walking, but it remains unknown whether this finding generalizes to other muscle groups and whether muscles become completely deafferented. In decerebrate cats at least 19 wk after nerve cut and repair, we examined the influence of quadriceps (Q) muscles' self-reinnervation on autogenic length feedback, as well as intermuscular length and force feedback, among the primary extensor muscles in the cat hindlimb. Effects of gastrocnemius and soleus self-reinnervation on intermuscular circuitry were also evaluated. We found that autogenic length feedback was lost after Q self-reinnervation, indicating that loss of the stretch reflex appears to be a generalizable consequence of muscle self-reinnervation. However, intermuscular force and length feedback, evoked from self-reinnervated muscles, was preserved in most of the interactions evaluated with similar relative inhibitory or excitatory magnitudes. These data indicate that intermuscular spinal reflex circuitry has the ability to regain functional connectivity, but the restoration is not absolute. Explanations for the recovery of intermuscular feedback are discussed, based on identified mechanisms responsible for lost autogenic length feedback. Functional implications, due to permanent loss of autogenic length feedback and potential for compensatory adaptations from preserved intermuscular feedback, are discussed.

Stretching did not alter joint angles or gastrocnemius muscle activity in the early to midstance phase of gait.