Comparison between animal and human studies of skeletal muscle adaptation to chronic stimulation.

Functional electrical stimulation (FES) has recently emerged as a clinical tool for treatment of neuromuscular disorders. Chronic muscle stimulation, however, has long been used by basic scientists studying the details of the muscular adaptation process. Biochemical, morphological, and functional changes occur in skeletal muscle secondary to chronic stimulation. Chronic stimulation (12-24 hours per day for six weeks) results in a well-defined progression of changes in which a "fast" muscle becomes a typical "slow" muscle with a large decrease in force-generating capacity. On the other hand, clinical studies of FES have demonstrated muscle strengthening following treatment. An attempt is made to reconcile the results obtained in the two fields.