Determination of critical power by pulmonary gas exchange.

Although the physiological underpinnings of critical power (CP) have yet to be fully elucidated, it has been proposed that CP demarcates the heavy and severe exercise intensity domains and that each domain is associated with a different pattern of metabolic response and mechanism of fatigue. Severe intensity has been defined such that, during exercise at intensities above CP, the slow component of the VO2 response will drive VO2 to VO2max at the point of fatigue. In this study, two parameters were derived for each of 8 participants: (a) CP, the asymptote of the relationship between power and time to exhaustion, and (b) a related parameter; CP', the asymptote of the relationship between power and time to VO2max. CP' theoretically represents the threshold intensity above which VO2max will be elicited during exercise of sufficient duration. Participants performed two exhaustive tests at CP. There were three important findings: First, there was a practice effect on time to exhaustion at CP, and times increase 27% in the second test. Second, both CP and CP' could be obtained with good precision. Third, and most important, CP was equal to CP', thereby providing a physiological description of the mathematically derived CP parameter. It was concluded that VO2max cannot be elicited at intensities equal to or less than CP.