Does the gas exchange anaerobic threshold occur at a fixed blood lactate concentration of 2 or 4 mM?

The anaerobic threshold (theta an) is defined as the VO2 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 congruent to 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 theta an to the three lactate criteria (break point, 2 mM, and 4 mM) for theta an 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 theta an determination: (1) systematic increase in VE/VO2, without a concomitant increase in VE/VCO2; (2) lactate break point; (3) 2 mM [lactate]; and (4) 4 mM [lactate]. Relative to the gas exchange criterion (i.e., #1), theta an was higher by 44, 280, and 1028 ml X min-1 for the three lactate criteria, respectively; the last two being significantly different (P less than 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.