THE &OV0312;O2 SLOW COMPONENT DURING REPEATED BOUTS HEAVY CYCLING EXERCISE IN HUMANS

Abstract

1681 In heavy exercise domain above θL, an "additional" V̇O2 (V̇O2 slow component; V̇O2-SC) superimposes the "expected" V̇O2 that projected from the linear sub-θL steady state V̇O2 (ssV̇O2)-work rate (WR) relation. It has repeatedly been shown that after prior heavy exercise, the V̇O2-kinetics of subsequent heavy exercise are faster. While such speeding is assumed to be closely linked to the V̇O2-SC, previous studies have evaluated it using only the conventional measure of the difference of V̇O2 between min 6 and 3 (ΔV̇O2(6-3)). Therefore, we evaluated the precise V̇O2-SC which is defined as the V̇O2 above that predicted on the basis of the sub-θL ssV̇O2-WR relation. Six healthy subjects participated in this study. The control was two consecutive 6-min exercise bouts at θF separated by 6-min baseline at 20 W. To determine the ssV̇O2-WR linear relation for the 1st and 2nd bout, each subject performed randomly more than three times 6-min moderate (i.e., sub-θL) exercises with or without 6-min prior heavy exercise at θF. In the control exercise, ΔV̇O2(6-3) for the 2nd bout were smaller than the 1st bout [1st: 201±92, 2nd: 97±52 mL·min−1; p<0.05]. For moderate exercise bouts, the ssV̇O2-WR slope for 2nd bout was higher than the 1st bout [1st: 9.43±0.42, 2nd: 10.46±0.81 mL·min−1·W−1; p<0.05], whereas the intercept had no difference. The slope difference increased the predicted ssV̇O2 for 2nd bout (p<0.05). For 1st heavy control bout, V̇O2-SC was larger than the predicted value [V̇O2 at min 6: 2369±318, 1st bout predicted ssV̇O2: 2100±349 mL·min−1; p<0.05]. In contrast, V̇O2-SC for 2nd heavy control bout was not different to the predicted value [V̇O2 at min 3 and 6: 2297±311 and 2394±324, 2nd bout predicted ssV̇O2: 2293±368 mL·min−1, ns]. It was concluded that V̇O2-SC during the 2nd bout of heavy exercise was not detected due to the upward shift of sub-θL ssV̇O2-WR relation. The underlying mechanisms are, however, presently unresolved. Supported in part by Grant-in-Aid for Scientific Research from The Ministry of Education, Science, Sports and Culture in Japan (#10680048).