A new method for detecting anaerobic threshold by gas exchange

TLDR

Excess CO₂ is produced during exercise when lactate rises, as its H⁺ is buffered mainly by bicarbonate. The authors sought to develop a computerized regression approach to detect the anaerobic threshold (AT) by analyzing the V‑slope of CO₂ versus O₂ uptake. They applied V‑slope regression to incremental exercise tests, identifying the point where CO₂ output exceeds the linear relationship with O₂ uptake, marking the onset of excess CO₂ from H⁺ buffering. In ten subjects, the V‑slope AT closely matched lactate and bicarbonate thresholds, agreed with visual determinations, and proved more reliable, while the respiratory compensation point was consistently higher than AT, demonstrating the method’s advantages over conventional techniques.

Abstract

Excess CO2 is generated when lactate is increased during exercise because its [H+] is buffered primarily by HCO-3 (22 ml for each meq of lactic acid). We developed a method to detect the anaerobic threshold (AT), using computerized regression analysis of the slopes of the CO2 uptake (VCO2) vs. O2 uptake (VO2) plot, which detects the beginning of the excess CO2 output generated from the buffering of [H+], termed the V-slope method. From incremental exercise tests on 10 subjects, the point of excess CO2 output (AT) predicted closely the lactate and HCO-3 thresholds. The mean gas exchange AT was found to correspond to a small increment of lactate above the mathematically defined lactate threshold [0.50 +/- 0.34 (SD) meq/l] and not to differ significantly from the estimated HCO-3 threshold. The mean VO2 at AT computed by the V-slope analysis did not differ significantly from the mean value determined by a panel of six experienced reviewers using traditional visual methods, but the AT could be more reliably determined by the V-slope method. The respiratory compensation point, detected separately by examining the minute ventilation vs. VCO2 plot, was consistently higher than the AT (2.51 +/- 0.42 vs. 1.83 +/- 0.30 l/min of VO2). This method for determining the AT has significant advantages over others that depend on regular breathing pattern and respiratory chemosensitivity.