ALTERATIONS IN OXYGEN-CONSUMPTION DURING AND BETWEEN BOUTS OF LEVEL AND DOWNHILL RUNNING

Since the etiology of the drift in VO2 during downhill running is uncl ear, this study was designed to assess the contribution of heart rate (HR) ventilation (V-E), blood lactate, rectal temperature (RT), muscle damage, and several variables that have not previously been included in VO2 drift research: muscle temperature (MT), and stride rate (SR) a nd length (SL), to the drift in VO2. Six subjects participated in a 45 -min level run (LEVEL) and two 45-min downhill runs (DOWN1 and DOWN2) at 50% VO2max. Although VO2 increased significantly over time for all bouts, the magnitude [4.3% (LEVEL), 5.4% (DOWN1), and 8.1% (DOWN2)] di d not differ between bouts (P > 0.05). VO2 was significantly lower dur ing 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 c reatine 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. V-E and blood lactate did nor d iffer over time or between bouts. VO2 drift during the three bouts par alleled changes in RT, MT, and HR but appears unrelated to muscle dama ge or biomechanical factors.