The purposes of this study were: (1) to compare the physiological responses during simulated wheelchair racing (SR) between male quadriplegics and paraplegics, (2) to test the validity of the SR against a track race (TR) and (3) to examine the relationship between the peak oxygen uptake (peak VO2) and wheeling velocity (WV) during the SR and TR. Seven quadriplegics (C5-8 lesions) and six paraplegics (T5-L4 lesions) completed (1) an incremental wheelchair velocity test, (2) a SR (1.6 km for quadriplegics and 3.2 km for paraplegics), and (3) an indoor TR of the same distance. The subjects performed the incremental velocity test and SR in their personal wheelchairs mounted on a roller system interfaced with customized software programmed to provide velocity and distance feedback. Physiological responses were monitored using an automated metabolic cart and electrocardiogram. Blood lactate concentration [La] was determined from finger prick samples. Peak VO2 and peak heart rate (peak HR) were significantly higher in the paraplegics compared to quadriplegics: 1.90 +/- 0.54 vs 1.07 +/- 0.35 l/min, and 188 +/- 11 beats/min vs 117 +/- 12 beats/min respectively. The paraplegics exercised at significantly (p < 0.05) higher percentages of peak VO2 and peak HR during the SR compared to quadriplegics (95% vs 76% and 95% vs 86%, respectively). No significant relationships (p < 0.05) were observed between the peak VO2 and WV during the SR and TR in either group.(ABSTRACT TRUNCATED AT 250 WORDS)