Purpose: We postulated that the relationship between [latin capital V with dot above]O2 and work rate ([latin capital V with dot above]O2-WR relationship) during incremental exercise is dependent on O2 availability, and that training-induced adaptations alter this relationship. We therefore studied the effect of endurance training on [latin capital V with dot above]O2 response during incremental exercise in normoxia and hypoxia (FIO2 = 0.134). Methods: Before and after training (6 d[middle dot]wk-1, 4 wk), eight subjects performed incremental exercises under normoxia and hypoxia and one constant-work rate exercise in normoxia at 80% of pretraining [latin capital V with dot above]O2max. The slopes of the [latin capital V with dot above]O2-WR relationship during incremental exercise were calculated using all the points (whole slope) or only points before the lactate threshold (pre-LT slope). The difference between [latin capital V with dot above]O2max measured and [latin capital V with dot above]O2max expected from the pre-LT slope ([DELTA][latin capital V with dot above]O2) was determined, as was the difference between [latin capital V with dot above]O2 at minute 10 and [latin capital V with dot above]O2 at minute 4 during the constant-work rate exercise ([DELTA][latin capital V with dot above]O2(10'-4')). Results: In normoxia, training induced a significant decrease in the whole slope (11.0 +/- 1.0 vs 9.9 +/- 0.4 mL[middle dot]min-1[middle dot]W-1, P < 0.05). In hypoxia, training induced a significant increase in the pre-LT slope (8.7 +/- 1.2 vs 9.8 +/- 0.7 mL[middle dot]min-1[middle dot]W-1; P < 0.05) and the whole slope (8.5 +/- 1.2 vs 9.4 +/- 0.5 mL[middle dot]min-1[middle dot]W-1; P < 0.05). A significant correlation between the decrease of [DELTA][latin capital V with dot above]O2 and the decrease of [DELTA][latin capital V with dot above]O2(10'-4') with training was found in normoxia (P < 0.01, r2 = 0.79). Conclusions: Taken together, these results indicate that adaptations induced by endurance training are associated with more efficient incremental and constant-workload exercise performed in normoxia. Moreover, training contributes to improved O2 delivery during moderate exercise performed in hypoxia, and to enhanced near-maximal exercise tolerance.
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