Reliability, reproducibility and validity of the individual anaerobic threshold.

The individual anaerobic threshold (IAT) has been defined as the highest metabolic rate at which blood lactate (La) concentrations are maintained at a steady state during prolonged exercise. The validity of this definition, however, has not been substantiated. Eleven men [maximum oxygen uptake (VO2max), mean (SD), 57.8 (6.9) ml.kg-1 x min-1) did two maximal incremental cycle exercise tests (30 W and 4 min per step). Blood was sampled repeatedly during exercise and for 9 min during the subsequent recovery period with light activity. The subjects then exercised at the power output equivalent of IAT for 45 min, until they could no longer continue or until rectal temperature reached 39 degrees C. Subjects performed two additional exercise tests. The intensity of these tests depended upon the LA and acid-base responses during the last 15 min of at least 30 min of exercise at IAT. If a steady state was achieved (La, pH and PCO2 changed by less than 0.5 mmol.l-1, 0.005 pH units and 0.3 kPa, respectively) or decreasing La and increasing pH values were observed, then the second test was performed at IAT +5% VO2max and the third session at either IAT +2.5% or +7.5% VO2max. Conversely if a steady state was not achieved during exercise at the calculated IAT, the intensity of the second test was set at IAT -5% VO2max. Depending on the La and acid-base responses during this test, the final session was performed at either IAT -2.5% or -7.5% VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)