Perhaps the hallmark study in human exercise physiology was performed by Nobel Laureate Professor AV Hill on himself in Manchester, England in the early 1920s. Hill circled an 88 metre grass running track at three different speeds each for 4 minutes while he measured his average oxygen consumption every 30 seconds (Hill and Lupton;1 fig 2 of that paper). He concluded that his oxygen consumption reached a maximum at 16 km/hour “beyond which no bodily effort can drive it”.2 (page 1661) This experiment established the single most popular test in the exercise sciences – the progressive exercise test for the measurement of the maximum oxygen consumption (VO_2max). The experimental protocol in this test forces the subject progressively to increase the work rate until voluntary exhaustion.

According to the modern interpretation,3^–14 the outcome of this test defines the limits of the human cardiorespiratory system, because it apparently terminates when the cardiac output reaches a maximum value.9 11 13 It also established a model to explain the biology of human exercise performance, for if the cardiovascular system determines maximal exercise performance, then it must also determine performance during many other forms of exercise, as suggested by Bassett and Howley9 and others.15 16 Thus, champion athletes able to run very fast for long distances do so because of the metabolic consequences in their skeletal muscles of their superior cardiovascular function,9 15 16 even though they exercise at intensities below that at which the VO_2max is reached and at which, according to that model, cardiovascular function is not maximal and cannot therefore, by definition, be the “limiting” factor.

This explanation seems paradoxical because, if correct, it predicts that athletes should be able to exercise more vigorously and for longer simply by increasing …