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Maximal oxygen uptake (V˙O2max) was defined by Hill and Lupton in 1923 as the oxygen uptake attained during maximal exercise intensity that could not be increased despite further increases in exercise workload, thereby defining the limits of the cardiorespiratory system. This concept has recently been disputed because of the lack of published data reporting an unequivocal plateau in V˙O2 during incremental exercise.The purpose of this investigation was to test the hypothesis that there is no significant difference between the V˙O2max obtained during incremental exercise and a subsequent supramaximal exercise test in competitive middle-distance runners. We sought to determine conclusively whether V˙O2 attains a maximal value that subsequently plateaus or decreases with further increases in exercise intensity.Fifty-two subjects (36 men, 16 women) performed three series of incremental exercise tests while measuring V˙O2 using the Douglas bag method. On the day after each incremental test, the subjects returned for a supramaximal test, during which they ran at 8% grade with the speed chosen individually to exhaust the subject between 2 and 4 min. V˙O2 at supramaximal exercise intensities (30% above incremental V˙O2max) was measured continuously.V˙O2max measured during the incremental test (63.3 ± 6.3 mL·kg−1·min−1; mean ± SD) was indistinguishable from the V˙O2max during the supramaximal test (62.9 ± 6.2, N = 156; P = 0.77) despite a sufficient duration of exercise to demonstrate a plateau in V˙O2 during continuous supramaximal exercise. These data provide strong support for the hypothesis that there is indeed a peak and subsequent plateau in V˙O2 during maximal exercise intensity.V˙O2max is a valid index measuring the limits of the cardiorespiratory systems' ability to transport oxygen from the air to the tissues at a given level of physical conditioning and oxygen availability.