A comparative evaluation of the individual anaerobic threshold and the critical power.

The individual anaerobic threshold (IAT) is defined as the highest metabolic rate where blood lactate (La) concentrations are maintained at a steady-state during prolonged exercise. The asymptote of the hyperbolic relationship between power output and time to fatigue has been defined as the critical power (CP), which, in theory, represents the highest metabolic rate where a steady-state response can be achieved during prolonged exercise. Since IAT and CP may define the same power output, the purpose of this study was to compare the gas exchange, blood La, and acid-base responses during exercise at the metabolic rates defined as IAT and CP. Fourteen males performed a maximal incremental cycle exercise test that was followed by a light active recovery period to determine IAT. Subsequently, subjects exercised to fatigue at five power outputs (calculated to elicit from 90% to 110% VO2max) to determine CP. IAT occurred at a significantly lower power output and VO2 (235 +/- 44 W and 2.97 +/- 0.47 l.min-1, respectively) compared with CP (265 +/- 39 W and 3.35 +/- 0.41 l.min-1, respectively). During 30 min of exercise at IAT, blood La levels increased during the initial 10 min to 3.9 +/- 1.9 mmol.l-1 but did not change during the final 15 min. Blood pH decreased to 7.32 +/- 0.04 at 5 min and did not change thereafter, while PCO2 fell from 41.5 +/- 3.2 mm Hg at 5 min to 36.2 +/- 3.6 mm Hg at 30 min. Only one subject completed 30 min of exercise at CP.(ABSTRACT TRUNCATED AT 250 WORDS)