Reliability, reproducibility and validity of the individual anaerobic threshold

Summary

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 ($\dot VO_{2max}$), mean (SD), 57.8 (6.9) ml·kg⁻¹ · 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°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% $\dot VO_{2max}$ and the third session at either IAT + 2.5% or +7.5% $\dot VO_{2max}$. 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% $\dot VO_{2max}$. Depending on the La and acid-base responses during this test, the final session was performed at either IAT −2.5% or −7.5% $\dot VO_{2max}$. Test-retest reliability for the determination of IAT was high (r = 0.98; estimated SE was 8 W or about 2% $\dot VO_{2max}$) and the method was reproducible [mean (SD); 240.3 (41.7) W for test 1 and 236.6 (42.9) W for test 2]. However, only 4 subjects completed at least 30 min of exercise at IAT with steady-state La and acid-base responses. None of these subjects showed steady-state responses at +5% $\dot VO_{2max}$ above IAT, and only 1 met the criteria at +2.5% $\dot VO_{2max}$ above IAT. Therefore, for these individuals the incremental exercise test underestimated the “true” IAT by less than 5% $\dot VO_{2max}$. For the other 7 subjects, 4 met the steady-state criteria at both −5% and −2.5% $\dot VO_{2max}$ below the calculated IAT, suggesting the true IAT was overestimated by less than 2.5% $\dot VO_{2max}$. For 2 of the remaining subjects, the incremental exercise test over-estimated the true IAT by at least 7.5% $\dot VO_{2max}$. Therefore, the maximal incremental exercise test followed by a light active recovery period will produce a reliable and reproducible estimate of IAT which is valid for the majority of subjects. However, since the method overestimates the true IAT for some individuals, the procedure cannot be assumed (without verification) to be valid for all subjects.