A longitudinal study of skeletal muscle following spinal cord injury and locomotor training

Study design: Experimental rat model of spinal cord contusion injury (contusion SCI). Objective: The objectives of this study were (1) to characterize the longitudinal changes in rat lower hindlimb muscle morphology following contusion SCI by using magnetic resonance imaging and (2) to determine the therapeutic potential of two types of locomotor training, treadmill and cycling. Setting: University research setting. Methods: After moderate midthoracic contusion SCI,Sprague- Dawley rats were assigned to either treadmill training, cycle training or an untrained group. Lower hindlimb muscle size was examined prior to SCI and at 1-, 2-, 4-, 8-, and 12- week post injury. Results: Following contusion SCI, we observed significant atrophy in all rat hindlimb muscles with the posterior muscles ( triceps surae and flexor digitorum) showing greater atrophy than the anterior muscles ( tibialis anterior and extensor digitorum). The greatest amount of atrophy was measured at 2- week post injury ( range from 11 to 26%), and spontaneous recovery in muscle size was observed by 4 weeks post-SCI. Both cycling and treadmill training halted the atrophic process and accelerated the rate of recovery. The therapeutic influence of both training interventions was observed within 1 week of training and no significant difference was noted between the two interventions, except in the tibialis anterior muscle. Finally, a positive correlation was found between locomotor functional scores and hindlimb muscle size following SCI. Conclusions: Both treadmill and cycle training diminish the extent of atrophy and facilitate muscle plasticity after contusion SCI.