Physiological responses during exercise to exhaustion at critical power

Critical power (CP) is a theoretical construct derived from a series of constant load tests to failure. Many studies have examined the methodological limitations of deriving CP, but few studies have examined the responses to exercise at CP in well-trained individuals. The purpose of the present study was to examine the physiological responses to exercise at CP. Seven male subjects [mean (SD) body mass 75.6 (6.4) kg, maximum oxygen uptake 4.6 (0.7) 1 min(-1)] performed three constant load tests to derive CP. Subjects then exercised at CP until volitional exhaustion. Heart rate, oxygen consumption and blood lactate concentration were measured throughout. Repeated measures analysis of variance revealed significant differences over time in heart rate 118 (24) to 177(5) beats min(-1), oxygen consumption 3.7 (0.6) to 4.1 (0.5) 1 min(-1) and blood lactate concentration 4.3 (1.8) to 6.5 (2.0) mM. All seven subjects completed 20 min of exercise with the range of time to failure at CP from 20 min 1 s to 40 min 37 s. Time to failure and maximum oxygen consumption were significantly correlated (r=0.779, P<0.05). We conclude, therefore, that CP does not represent a sustainable steady-state intensity of exercise.