Unexpected Fascicle Length Changes In Denervated Feline Soleus Muscle During Stance Phase Of Walking.

Ricky Mehta,Huub Maas,Boris I Prilutsky,Robert J Gregor

doi:10.1038/srep17619

Abstract

After surgical repair of traumatically severed peripheral nerves, associated muscles are paralyzed for weeks. Little is known about fascicle length changes in paralyzed muscles during locomotion. The aim of this study was to investigate to what extent, if any, muscle fascicles of denervated feline soleus (SO) change length during stance of walking when intact SO synergists are actively contracting. Hindlimb kinematics, SO fascicle and muscle-tendon unit (MTU) length, and EMG activity of SO, lateral gastrocnemius (LG) and medial gastrocnemius (MG) were measured during level and slope walking in adult cats. Measurements were taken before and 1–2 weeks following SO-LG denervation. Unexpectedly, SO fascicle lengthening and shortening during stance in all walking conditions were evident after denervation. The greatest SO fascicle shortening (17.3 ± 2.2% of a reference length) and least fascicle lengthening (1.5 ± 0.8%) after denervation were found during upslope walking, where MG EMG activity was greatest across slopes (P < 0.05) and greatest discrepancies between post denervation SO fascicle and MTU length changes occurred. These findings suggest that myofascial linkages between denervated SO and its active synergists might affect its fascicle length changes. Further studies are needed to directly test this suggestion.

Highlights

After surgical repair of traumatically severed peripheral nerves, associated muscles are paralyzed for weeks
After surgical repair of a severed peripheral nerve, the muscle remains in a state of paralysis while motor and sensory axons from the proximal nerve stump are regenerating at a rate of 1–3 mm/day to reach the target muscle[5,6]
During days 3 to 14 after SO-lateral gastrocnemius (LG) nerve transection and repair, SO and LG muscles were paralyzed, which was evident from the lack of EMG bursts during walking (Fig. 1)

Summary

Introduction

After surgical repair of traumatically severed peripheral nerves, associated muscles are paralyzed for weeks. The aim of this study was to investigate to what extent, if any, muscle fascicles of denervated feline soleus (SO) change length during stance of walking when intact SO synergists are actively contracting. Of a reference length) and least fascicle lengthening (1.5 ± 0.8%) after denervation were found during upslope walking, where MG EMG activity was greatest across slopes (P < 0.05) and greatest discrepancies between post denervation SO fascicle and MTU length changes occurred These findings suggest that myofascial linkages between denervated SO and its active synergists might affect its fascicle length changes. After surgical repair of a severed peripheral nerve, the muscle remains in a state of paralysis while motor and sensory axons from the proximal nerve stump are regenerating at a rate of 1–3 mm/day to reach the target muscle[5,6] During this time, the paralyzed muscle is prone to atrophy[7,8]. Paralysis of selected ankle extensors in animal models changes inter-joint coordination as well as activity and fascicle length changes in intact synergists[12,13,14,15]

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