Differences in End-Point Force Trajectories Elicited by Electrical Stimulation of Individual Human Calf Muscles

The purpose of this study was to investigate the end-point force trajectories of the fibularis longus (FIB), lateral gastrocnemius (LG) and medial gastrocnemius (MG) muscles. Most information about individual muscle function has come from studies which use models based on electromyographic (EMG) recordings. In this study (N=20 subjects) we used electrical stimulation (20Hz) to elicit activity in individual muscles, recorded the end-point forces at the foot and verified the selectivity of stimulation by using magnetic resonance imaging. Unexpectedly, no significant differences were found between LG and MG force directions. Stimulation of LG and MG resulted in downward and medial or lateral forces depending on the subject. We found FIB end-point forces to be significantly different than those of LG and MG. In all subjects, stimulation of FIB resulted in downward and lateral forces. Based on our results, we suggest that there are multiple factors determining when and whether LG or MG will produce a medial or lateral force and FIB consistently plays a significant role in eversion/abduction and plantarflexion. We suggest that the inter-subject variability we found is not simply an artifact of experimental or technical error but is functionally relevant and should be addressed in future studies and models

Local Loss of Proprioception Results in Disruption of Interjoint Coordination During Locomotion in the Cat

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

Local Loss of Proprioception Results in Disruption of Interjoint Coordination During Locomotion in the Cat

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

Local Loss of Proprioception Results in Disruption of Interjoint Coordination During Locomotion in the Cat

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