The effects of body-weight supported treadmill training on cardiovascular regulation in individuals with motor-complete SCI

Study design: Four-month longitudinal within-subject exercise training study.

Objective: Although body-weight supported treadmill training (BWSTT) has not shown promise as a means of improving ambulation in individuals with motor-complete spinal cord injury (SCI), it may still improve cardiovascular health and function in this population. The purpose of this study was to (i) investigate the effects of BWSTT on peripheral muscular and elastic artery dimension and function and measures of heart rate variability (HRV) and blood pressure variability (BPV) in individuals with motor-complete SCI, and (ii) to make a preliminary examination of what factors may predict favourable cardiovascular outcomes following BWSTT in this population.

Setting: Centre for Health Promotion and Rehabilitation, McMaster University, Hamilton, Ontario, Canada.

Methods: Six individuals (four male, two female; age 37.7+/-15.4 years) with chronic SCI (C4-T12; ASIA A-B; 7.6+/-9.4 years post-injury) were included in the present investigation. Doppler ultrasound was used to determine femoral (exercising; muscular), carotid (elastic) and brachial (non-exercising control; muscular) artery dimension and function before and after 4 months of BWSTT. Continuous heart rate and blood pressure were also recorded before and after 4-months of BWSTT to determine frequency domain measures of HRV and BPV; clinically valuable indices of neurocardiac and neurovascular control, respectively.

Results: Two-way ANOVA (vessel x time) revealed no exercise-induced change in femoral or carotid artery cross-sectional area, blood flow or resistance and no change in carotid artery compliance following the 4 months of BWSTT compared to the non-exercising control brachial artery. However, there was a significant exercise-induced increase in femoral artery compliance. There were no exercise-induced changes in HRV or BPV when all participants were considered together. However, the results suggest that the subgroup of individuals who had a substantial heart rate response to BWSTT (n=3), experienced exercise-training induced changes in HRV reflective of a relative shift toward cardiac vagal predominance and reductions in BPV.

Conclusions: BWSTT may cause an increase in femoral artery compliance in individuals with motor-complete SCI and therefore, should be encouraged as a means of improving cardiovascular health in this population. BWSTT may also cause modest improvements in measures of HRV and BPV in a select subgroup of individuals who respond to ambulation with moderate to large increases in HR. In the present study, factors associated with a substantial HR response to BWSTT were a propensity to orthostatic intolerance and muscular spasticity.