CHANG, Y.-H.; SCHOLZ, J.P.; NICHOLS, T.R.; Emory University & Georgia Institute of Technology, Atlanta; University of Delaware, Newark; Emory University, Atlanta: Hindlimb Control during Cat Locomotion after Loss of Stretch Reflexes.

Locomotion in legged vertebrates involves the coordinated movement of the limbs. In addition to voluntary actions, involuntary actions produced by muscle stretch reflexes also help coordinate limb movements. Passive biomechanical constraints further provide the context within which both voluntary and involuntary actions affect movement. We studied the relative role of stretch reflexes during locomotion by using a surgical intervention to selectively remove stretch reflexes from select muscles of the cat hindlimb. We then quantified kinematic deficits during locomotion associated with the loss of this reflex. Self-reinnervation (SR) of muscle following surgical nerve transection and repair results in the functional loss of stretch reflexes to that muscle. Our goal was to quantify the neuromechanical influence of short-latency proprioceptive feedback from different ankle extensors over a range of speeds (0.4-2.0 m/s) and gaits (walk and trot). Any resulting deficits in single or multi-joint kinematics corresponded to a reliance on proprioceptive feedback from the affected muscle during the specific locomotor task. We also used the Uncontrolled Manifold approach of Scholz and Sch�ner (1999) to test if any changes in global limb control occurred after muscle SR. Preliminary results (N=3) suggest that the stretch reflex from ankle extensor muscles helped to maintain ankle joint stiffness during early stance phase of locomotion. Stretch reflexes were important for coordinating joint dynamics between the knee joint and the ankle joint during mid-stance. Global hindlimb control strategy appeared to be affected by the loss of stretch reflexes from ankle extensor muscles. These findings each were muscle-specific as well as speed-specific.