Limits to maximal performance in individuals with spinal cord injury

The purpose of this study was to examine the effect of four conditions that might improve oxygen transport and/or utilization during maximal exercise performance in individuals with spinal cord injury (SCI). Five males with tetraplegia (TP) and four males with paraplegia (PR) performed maximal arm cranking exercise in the following positions: 1) sitting; 2) supine; and 3) sitting with the addition of a) anti-gravity suit (anit-G), b) elastic stockings and abdominal binder, and c) functional electrical stimulation (FES) of the paralysed leg muscles. Peak power output (PO peak), peak oxygen uptake (VO2peak), peak heart rate (HR peak) and maximal systolic blood pressure were significantly lower in TP compared to PR for all conditions. A significant decrease in HR peak for PR, and a significant increase in VO2peak/kg for TP was seen during the supine compared to sitting condition. Respiratory exchange ratio (R) decreased significantly during the FES compared to the sitting condition in TP. No other changes were observed for any of the other conditions in either group. Improvements in central circulation previously reported during submaximal exercise for these four conditions did not result in a concomitant rise in maximal exercise performance. The results of this study suggest that the limitation in VO2peak for individuals with SCI is located peripherally (small active muscle mass) rather than centrally (heart or lungs).