Therapeutic stimulation of denervated muscles: the influence of pattern.

Muscular atrophy due to denervation can be substantially reversed by direct electrical stimulation. Some muscle properties are, however, resistant to change. Using a rabbit model of established denervation atrophy, we investigated whether the extent of restoration would vary with the stimulation protocol. Five patterns, delivering 24,000-480,000 impulses/day, were applied for 6 or 10 weeks. The wet weight, cross-sectional area, tetanic tension, shortening velocity, and power of denervated muscles subjected to stimulation all increased significantly. The fibers were larger and more closely packed and there was no evidence of necrosis. There was a small increase in excitability. Isometric twitch kinetics remained slow and fatigue resistance did not improve. The actual pattern of stimulation had no influence on any of these findings. The results, interpreted in the context of ultrastructural changes and an ongoing clinical study, reaffirm the clinical value of introducing stimulation during the initial non-degenerative phase. They indicate that there would be little therapeutic benefit in adopting regimes more energetically demanding than those in current use, and that the focus should now shift to protocols that represent the least intrusion into activities of daily living.