The effects of therapeutic electric stimulation on acute muscle atrophy in rats after spinal cord injury.

OBJECTIVE

To evaluate the effects of electric stimulation in preventing acute muscle atrophy after spinal cord transection in rats.

DESIGN

A randomized experimental design.

SETTING

Animal facilities for experimental medicine.

ANIMALS: Fifty-six adult male Wistar rats assigned to control, low-frequency, and high-frequency groups.

INTERVENTIONS: The rats were implanted with a percutaneous intramuscular electrode in the vicinity of the peroneal nerve; then the spinal cord was transected in a T9 level. The stimulation frequency was low (20Hz) or high (100Hz). The stimulation cycle was 4 seconds of stimulation every 8 seconds.

MAIN OUTCOME MEASUREMENTS: The lesser fiber diameters from type 1, 2A, and 2B muscle fibers were measured. In another assessment, maximal contraction force was measured. The muscle force produced at 20 and 100Hz was expressed as increasing values in tetanic force.

RESULTS

Comparison between nonstimulated and stimulated tibialis anterior muscles found that atrophy of type 1 fibers (p < .01) and type 2B fibers (p < .05) at both stimulated levels and of type 2A fibers at 100-Hz level (p < .05) was prevented by therapeutic electric stimulation (TES). There were significant differences in the size of muscle fiber diameter between nonstimulated and stimulated muscles at 100Hz in type 2A and, markedly, in type 2B. The increasing value of muscle force was significantly greater at 100Hz than at 20Hz (p < .05). No significant histologic differences were observed between high- and low-frequency stimulated fibers of any of the 3 muscle types.

CONCLUSIONS

Acute atrophy of muscle fibers was more effectively prevented by high-frequency stimulation (100Hz) than by no stimulation or low-frequency stimulation (20Hz). The increasing value of muscle force was significantly greater at high-frequency than low-frequency stimulation, suggesting that the clinical application of high-frequency stimulation in acute spinal cord injury should be studied.