We tested the hypothesis that time course of O (2) uptake (VO (2)) measured during a supramaximal exercise performed in the field is driven to maximal oxygen uptake (VO (2max)). On an outdoor track, five middle-distance male runners first performed a test to determine VO (2max) and a supramaximal 800-m running test at least two days apart. VO (2) response was measured from the start to the end of exercise with the use of a miniaturised telemetric gas exchange system (Cosmed K4). VO (2max) was reached by all subjects 45 +/- 11 s (mean +/- SD) after the onset of the 800-m race (i.e., 316 +/- 75 m), and was maintained during the next 33 +/- 6 s (i.e., 219 +/- 41 m). The mean relative exercise intensity of the 800 m was 120 % VO (2max). An unexpected significant decrease in VO (2) (24.1 +/- 7.0 %; p < 0.05) was observed in all subjects during the final 38 +/- 17 s (i.e., the last 265 +/- 104 m). We concluded that, at onset of a simulated 800 m running event, VO (2) is quickly projected towards the VO (2max), and then becomes limited by the achievable VO (2max). This race profile shown by all athletes is in some contrast to what can be expected from earlier findings in a laboratory setting.