Autonomic Function and Exercise Performance in Elite Athletes with Cervical Spinal Cord Injury

Abstract

"Complete" cervical spinal cord injury (SCI) is commonly believed to cause the decentralization of spinal sympathetic circuits and a consequent inability to meet the hemodynamic demands of exercise. Recently, however, we have noticed that athletes with motor complete cervical SCI exhibit an exercise-induced tachycardia that appears to be at odds with the known effects of sympathetic decentralization. This study aimed to determine the physiological basis of this response and, in doing so, to investigate associations between autonomic function, International Wheelchair Rugby Federation (IWRF) classification, and indices of exercise performance in highly trained athletes. Seven Paralympic wheelchair rugby players with motor complete cervical SCI were firstly classified according to IWRF classification, then assessed for autonomic function (sympathetic skin response [SSR]) and cardiovascular function (systolic blood pressure in response to sit-up tilt). Next, HRpeak and distance covered during a field-based maximal 4-min push were measured. Finally, peak oxygen uptake (VO2peak) and HRpeak during laboratory-based maximal incremental arm-crank exercise were measured. All athletes demonstrated intact SSR (2.7 ± 1.2 responses from five stimulations), little or no change in systolic blood pressure in response to sit-up tilt (-22 ± 16 mm Hg), and exercise-induced tachycardia (HRpeak = 152 ± 20 bpm). SSR was significantly correlated with HRpeak in the field, 4-min push distance, and VO2peak (all ρ ≥ 0.946), whereas current IWRF classification was not. All participants exhibited partial preservation of descending sympathetic control. We also found that the degree of remaining SSR, but not IWRF classification, was strongly correlated with indices of exercise performance. The findings suggest that the degree of remaining sympathetic control is an important determinant of exercise performance in athletes with cervical SCI.