Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold.

Anaerobic threshold has been defined as the oxygen uptake (VO2) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (ATLa), (2) systematic increase in ventilatory equivalent for O2 with no change in the ventilatory equivalent for CO2 (ATVE/VO2), and (3) non-linear increase in expired ventilation graphed as a function of VO2 (ATVE). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same VO2 as the ATLa. The highest correlation between a gas exchange anaerobic threshold and ATLa was found for ATVE/VO2 and was r = 0.63 (P less than 0.05). These data provide evidence that the ATLa and ATVE do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the ATLa.