This study aimed to investigate the oxygen uptake and metabolic responses during a 400-m run reproducing the pacing strategy used in competition. A portable gas analyser was used to measure the oxygen uptake VO2 of ten specifically trained runners racing on an outdoor track. The tests included an incremental test to determine maximal VO2max and the velocity associated with, VO2maxv-VO2max a maximal 400-m and a 300-m running test. Blood lactate, bicarbonate concentrations HCO3- pH and arterial oxygen saturation were analysed at rest and 1, 4, 7, 10 min after the end of the 400 m and 300 m. The peak VO2 recorded during the 400T corresponded to 93.9 ± 3.9% of VO2max and was reached at 24.4 ± 3.2 s (192 ± 22 m). A significant decrease in VO2(P < 0.05) was observed in all subjects during the last 100 m, although the velocity did not decrease below v-VO2max. The VO2 in the last 5 s was correlated with the pH (r = 0.86, P < 0.0005) and HCO3- (r = 0.70, P < 0.05) measured at the end of 300T. Additionally, the velocity decrease observed in the last 100 m was inversely correlated with HCO3- and pH at 300T (r = -0.83, P < 0.001, r = -0.69, P < 0.05, respectively). These track running data demonstrate that acidosis at 300 m was related to both the VO2response and the velocity decrease during the final 100 m of a 400-m run.
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