Physiologic responses of elite paraplegic road racers to prolonged exercise

The purpose of this study was to determine cardiopulmonary and selected metabolic responses in spinal cord injured (SCI) paraplegics during prolonged arm crank exercise (ACE). Six male and one female elite SCI paraplegic (T4-12 lesions) road racers performed 40 continuous minutes of ACE at 60% of peak ACE oxygen uptake (VO2). Blood samples (30 ml) were collected via antecubital venipuncture at rest and minutes 20 and 40 of ACE for determinations of hemoglobin, hematocrit, serum free fatty acid (FFA), and blood lactate (LA) concentrations. No significant differences were observed over time for VO2 or pulmonary ventilation. Heart rate recorded at minutes 30 and 40 was significantly elevated above HR at minutes 10 and 20 of ACE indicating the presence of an upward drift in HR in paraplegics performing prolonged ACE. Compared to rest, LA concentration was significantly higher at minute 20 and remained relatively stable thereafter. A significant increase in FFA concentration at minute 40 combined with a significant decline in the respiratory exchange ratio suggested a preference for lipid substrate utilization by exercising muscle as ACE continued. The data indicate that the autonomic sympathetic nervous system impairment associated with paraplegia had no apparent adverse effects on cardiopulmonary or metabolic adjustments to prolonged ACE in these well-trained subjects.