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.3s-1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O2), normoxic (21% O2), or hyperoxic (40% O2) air. The anaerobic threshold was estimated from respiratory gas exchange threshold (RGET). Prior to the RGET, the delta VO2/delta WR was greater under normoxic [mean (SD); 10.19(1.04) ml O2.min-1.W-1] and hyperoxic [10.44 (0.72)] conditions compared with 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 indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the delta VO2/delta WR and response time was constant. Above the RGET, the normoxic VO2 response was the net result of a declining delta VO2/delta WR and a longer response time to the unsteady state character of a ramp exercise protocol.