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

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 V̇_E/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.

Key words

Ventilatory equivalents for V̇O₂ and V̇CO₂ - excercise-induced lactic acidosis - human subjects - bicycle ergometer