Ergogenic effects of spinal cord stimulation on exercise performance following spinal cord injury

Abstract

Abstract Importance: Cervical or upper-thoracic spinal cord injury (SCI, ≥T6) often leads to low resting blood pressure and impaired cardiovascular responses to acute exercise due to disrupted supraspinal sympathetic drive. Epidural (invasive, ESCS) and transcutaneous spinal cord stimulation (non-invasive, TSCS) have been used to target sympathetic circuits and modulate cardiovascular responses, yet their impact on submaximal upper-body exercise performance in individuals with SCI is unknown. Objective To compare the effects of cardiovascular-optimised ESCS and TSCS versus sham ESCS and TSCS on modulating cardiovascular responses and improving submaximal upper-body exercise performance in individuals with SCI. Design: Double-blinded, randomised comparison trial. Setting: Research center. Participants: Seven males with a chronic, motor-complete SCI between C6-T4, underwent a mapping session to identify cardiovascular responses to spinal cord stimulation. Subsequently, four participants (two ESCS and two TSCS) completed submaximal exercise testing. Exposures: Stimulation parameters (waveform, frequency, intensity, epidural electrode array configuration, specific transcutaneous electrode locations in the lumbosacral region) were optimized to elevate cardiovascular responses (CV-SCS). A sham condition (SHAM-SCS) served as a comparison. Participants performed arm-crank exercise to fatigue at a fixed workload corresponding to above ventilatory threshold, on separate days, with CV-SCS or SHAM-SCS. Main Outcomes and Measures: The primary outcome was time to fatigue during submaximal exercise. Heart rate and gas exchange variables were recorded throughout exercise and used to calculate oxygen pulse (a surrogate for stroke volume, SV). Blood pressure (BP) was monitored before exercise (pre-post applying stimulation). Rating of perceived exertion (RPE) was recorded every 5-min. Results CV-SCS increased resting BP, left ventricular cardiac contractility and total peripheral resistance. CV-SCS increased time to fatigue with ESCS and TSCS, relative to SHAM-SCS. Relative to baseline, change in systolic BP at rest was greater with CV-SCS versus SHAM-SCS. Peak oxygen pulse during exercise was greater with CV-SCS relative to SHAM-SCS. Furthermore, RPE tended to be lower with CV-SCS than SHAM-SCS during exercise. Conclusions and Relevance: Comparable improvements in time to fatigue with ESCS and TSCS suggest that both approaches could be promising ergogenic aids to support exercise performance or rehabilitation, along with reducing fatigue during activities of daily living in individuals with SCI.