Comparison of Single Bout Effects of Bicycle Training Versus Locomotor Training on Paired Reflex Depression of the Soleus H-Reflex After Motor Incomplete Spinal Cord Injury

Comparison of single bout effects of bicycle training versus locomotor training on paired reflex depression of the soleus H-reflex after motor incomplete spinal cord injury. Objective: To examine paired reflex depression changes post 20-minute bout each of 2 training environments: stationary bicycle ergometer training (bicycle training) and treadmill with body weight support and manual assistance (locomotor training). Design: Pretest-posttest repeated-measures. Setting: Locomotor laboratory. Participants: Motor incomplete SCI (n=12; mean, 44 +/- 16y); noninjured subjects (n=11; mean, 30.8 +/- 8.3y). Intervention: All subjects received each type of training on 2 separate days. Main Outcome Measure: Paired reflex depression at different interstimulus intervals (10s, 1s, 500ms, 200ms, and 100ms) was measured before and after both types of training. Results: (1) Depression was significantly less post-SCI compared with noninjured subjects at all interstimulus intervals and (2) post-SCI at 100-millisecond interstimulus interval: reflex depression significantly increased postbicycle training in all SCI subjects and in the chronic and spastic subgroups (P<.05). Conclusions: Phase-dependent regulation of reflex excitability, essential to normal locomotion, coordinated by pre- and postsynaptic inhibitory processes (convergent action of descending and segmental inputs onto spinal circuits) is impaired post-SCI. Paired reflex depression provides a quantitative assay of inhibitory processes contributing to phase-dependent changes in reflex excitability. Because bicycle training non-nalized reflex depression, we propose that bicycling may have a potential role in walking rehabilitation, and future studies should examine the long-term effects on subclinical measures of reflex activity and its relationship to functional outcomes.