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

Abstract

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 (10 s, 1 s, 500 ms, 200 ms, and 100 ms) 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 normalized 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.