Does the Gas Exchange Anaerobic Threshold Occur at a Fixed Blood Lactate Concentration of 2 or 4 mM?

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Abstract
The anaerobic threshold (θan) is defined as the V̇O2 at which blood lactate concentration [lactate] begins to systematically increase (lactate “break point”) during incremental exercise. Numerous studies have shown that gas exchange break points at the anaerobic threshold correlate highly (r ≃ 0.90) with the lactate break point. Recently, it has been suggested that the anaerobic threshold occurs at a fixed [lactate] of 2 mM or 4 mM. We therefore compared the gas exchange θ an to the three lactate criteria (break point, 2 mM, and 4 mM) for θan estimation. Fourteen subjects performed an incremental cycle ergometer test. Ventilation and gas exchange were computed every 30 s. During the same 30-s intervals, venous blood was sampled for [lactate]. Four criteria were used for flan determination: (1) systematic increase in V̇E/VαO2, without a concomitant increase in V̇E/V̇CO2; (2) lactate break point; (3) 2 mM [lactate]; and (4) 4 mM [lactate]. Relative to the gas exchange criterion (i.e., #1), θan was higher by 44, 280, and 1028 ml · min-1 for the three lactate criteria, respectively; the last two being signficantly different (P < 0.05). Thus, the anaerobic threshold discerned from gas exchange or the lactate break point does not correspond with a fixed, absolute [lactate] of 2 mM or 4 mM.

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