Since the etiology of the drift in [latin capital V with dot above]O2 during downhill running is unclear, this study was designed to assess the contribution of heart rate (HR), ventilation (VE), blood lactate, rectal temperature (RT), muscle damage, and several variables that have not previously been included in [latin capital V with dot above]O2 drift research: muscle temperature (MT), and stride rate (SR) and length (SL), to the drift in [latin capital V with dot above]O2. Six subjects participated in a 45-min level run (LEVEL) and two 45-min downhill runs (DOWN1 and DOWN2) at 50% [latin capital V with dot above]O2max. Although [latin capital V with dot above]O2 increased significantly over time for all bouts, the magnitude [4.3% (LEVEL), 5.4% (DOWN1), and 8.1% (DOWN2)] did not differ between bouts (P > 0.05). [latin capital V with dot above]O2 was significantly lower during DOWN2 than during LEVEL and DOWN1 (P < 0.05). MT increased during the three bouts (P < 0.05) but the change over time was not different between bouts. SR and SL did not change over time within each bout nor between the two downhill runs. Muscle damage, as indicated by serum creatinc kinase levels and perceived soreness, was less following LEVEL and DOWN2 than DOWN1 (P < 0.05). HR and RT increased over time (P < 0.05) but did not differ between bouts. VE and blood lactate did not differ over time or between bouts. [latin capital V with dot above]O2 drift during the three bouts paralleled changes in RT, MT, and HR but appears unrelated to muscle damage or biomechanical factors.
(C)1994The American College of Sports Medicine