Chronic stimulation accelerates functional recovery of immobilized soleus muscles of the rabbit

Unilateral immobilization of rabbit hindlimbs was carried out for 2 weeks with an ankle angle of 90 deg. This was followed either by natural recovery for a further 2 or 4 weeks, or by chronic electrical stimulation of the soleus nerve during 2 weeks recovery using a low-frequency pattern of activation. Immobilization caused gross degeneration and functional disruption of soleus. Mean fibre area was reduced by 60% compared with unoperated controls, twitch and tetanic tensions by 90% and there was speeding of the rising phase of contraction. Natural recovery for 2 weeks had little effect; some regeneration occurred but muscle fibres remained atrophied and immature as indicated by the histochemical expression of both fast and slow myosin. Function continued to be grossly impaired, twitch and tetanic tensions were 66 and 79% reduced and the time-to-peak twitch tension 31% faster than controls. Prolonging the natural recovery period to 4 weeks increased muscle fibre area to 60% of normal, and increased the acquisition of mature staining properties but most functional characteristics remained impaired. Stimulated muscles had normal fibre areas, mature appearance and functional improvements which matched and in most cases exceeded those seen after natural recovery for 4 weeks. Thus chronic low-frequency stimulation of soleus muscles accelerates recovery of structure and function following degenerative immobilization atrophy and may represent an important therapeutic aid in patient rehabilitation.