SUMMARY

Neural feedback pathways arise from a variety of sensory receptors. The firing of muscle spindles is nonlinearly related to length and velocity, while Golgi tendon organs measure active contractile force. Understanding the functions of these pathways during voluntary movement is important because they become disrupted in Spinal Cord Injury (SCI) and stroke. Most spindle pathways are relatively localized, but some are inter-joint. These inter-joint pathways may play a role in regulating whole limb properties. Experiments have shown that force-dependent feedback can be widely distributed and asymmetric between a given muscle pair. Additionally, force feedback is modulated according to the task and condition, such as slope walking and SCI. Although the muscle-level distributions of force feedback in the feline hindlimb have been measured under different conditions, it is not known how these distributions regulate limb mechanics (impedance and inter-joint coordination). With intrinsic viscoelastic properties incorporated into the joints, the goal of aim 1 is to investigate the influence of muscle spindle and Golgi tendon organ feedback on the impedance regulation of a single joint. The goal of aim 2 is to evaluate the role of excitatory monosynaptic spindle feedback in regulating whole limb impedance and inter-joint coordination. The goal of aim 3 is to evaluate the influence of force-dependent feedback on the regulation of whole limb impedance and on inter-joint coordination.