THE INFLUENCE OF INSPIRED OXYGEN ON THE OXYGEN-UPTAKE RESPONSE TO RAMP EXERCISE

The relation between VO2 and work rate (WR) was examined in seven male subjects who performed ramp (1 W . 3 s(-1)) two-legged cycle ergometr y to exhaustion while inspiring either hypoxic (12% O-2), normoxic (21 % O-2), or hyperoxic (40% O-2) air. The anaerobic threshold was estima ted from respiratory gas exchange data and is thus referred to as the respiratory gas exchange threshold (RGET). Prior to the RGET, the Delt a VO2/Delta WR was greater under normoxic [mean (SD); 10.19 (1.04) ml O-2 . min(-1). W-1] and hyperoxic [10.44 (0.72)] conditions compared w ith hypoxia [9.34 (0.89)]. Above the RGET, the Delta VO2/Delta WR for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 ( 0.48)] were all significantly different from each other. These data in dicated that for two-legged, cycle, ramp ergometry in normoxia below t he RGET, both the Delta VO2/Delta WR and response time was constant. A bove the RGET, the normoxic VO2 response was the net result of a decli ning Delta VO2/Delta WR and a longer response time to the unsteady sta te character of a ramp exercise protocol.