Time-based V-slope for determination of anaerobic threshold.

Background: The standard method for determining the noninvasive anaerobic threshold (AT) is the V-slope (VS) method. It is often supplemented by the ventilatory equivalent (VEQ) and end-tidal (ET) methods. However, a comparison issue arises: VS plots VCO Methods: V-slope is drawn as a square with equal sides, with the diagonal line representing the respiratory exchange ratio (R) = 1. V-slope generally follows the R = 1 line. This provides a framework in which the vertical difference (d) between a VCO Results: The mean AT (mL/min) and detection rates for d, VS, VEQ, and ET were 857 ± 414 (93%), 939 ± 407 (96%), 946 ± 176 (82%), and 862 ± 379 (85%), respectively. The d method identified AT significantly earlier than the conventional VS did ( Conclusions: The time-based V-slope was created by plotting changes in VCO2 from the R = 1 diagonal line against time; it aligned all three AT detecting methods on the same time axis, allowing precise detection of differences between methods. It also made AT detection more reliable, probably because the upward inflection breakpoint arises from the flat baseline and does not have the overlapping data points seen in V-slope, making it easier to identify a breakpoint. The d graph also identified AT significantly earlier than V-slope did.