Effects of exercise on autonomic cardiovascular control in individuals with chronic, motor-complete spinal cord injury: an exploratory randomised clinical trial

Study Design: Secondary analysis of a clinical trial. Objective: To assess the impact of 6 months of arm-cycle ergometer training (ACET), or body weight supported treadmill training (BWSTT), on autonomic cardiovascular responses to a laboratory sit-up test (SUT) in individuals with chronic (≥1-year post-injury) spinal cord injury (SCI). Setting: Canada. Methods: Sixteen individuals with motor-complete (American Spinal Injury Association Impairment Scale A-B) SCI between the fourth cervical and sixth thoracic spinal cord segments, aged 39±11 years, were assessed. Participants were randomized to receive 72 sessions of moderate-to-vigorous intensity ACET (n=8) or passive BWSTT (n=8). Changes in mean arterial pressure (MAP; finger plethysmography), hemodynamics (Modelflow® method), and heart rate/heart rate variability (HR/HRV; electrocardiography) were measured in response to SUT before and after 6 months of exercise training. Spontaneous cardiovagal baroreflex sensitivity (cvBRS) was assessed using the sequence method. Results: Neither ACET nor BWSTT impacted hemodynamic responses to SUT or the incidence of orthostatic hypotension (all P>0.36). ACET led to increased HR and high frequency (HF) power HRV responses (interaction effects, both P<0.01) to SUT following 6 months of training compared to BWSTT. Consistent with this, cvBRS improved (P<0.05) following ACET but not BWSTT. At the group level, improvements in cvBRS were highly correlated with both the HR (r=0.726, P<0.0001) and HF power (R=-0.484, P<0.01) responses to SUT. Conclusion: Six months of exercise training had no effect on BP responses to SUT in individuals with SCI. However, ACET, but not BWSTT, improved cardiovagal baroreflex control of HR in individuals with chronic, motor-complete SCI, suggesting benefits of volitional upper-body exercise. Clinical Trial Registration: NCT01718977