Computer Analysis of Oxygen Consumption and Minute Ventilation for the Detection of the Lactate Threshold

Abstract

A group of 15 normal subjects performed a maximal-exercise test on a treadmill. Arterial lactate measurements were related to oxygen consumption (VO₂) in an exponential fashion (individual correlation coefficients ranged from 0.9 to 0.99). In the same subjects, minute ventilation (VE) was related to VO₂ in an exponential fashion (individual correlation coefficients ranged from 0.98 to 1). There was a close correlation (r = 0.97, p < 0.001) between the slope of the log of lactate versus VO₂ and the slope of the log of VE versus VO₂. A computer program for predicting the VO₂ corresponding to the accumulation of arterial lactate above the resting normal value (1.3 m M), defined as the lactate threshold, is described. The program is based on the slopes of the exponential relationship between lactate and VO₂ and between VE and VO₂ derived in the normal subjects. The program analyses 30-second values of VO₂ and VE. In 28 subjects, the reproducibility of the lactate threshold prediction was evaluated during two exercise tests 1–7 days apart. The mean predicted VO₂ at the lactate threshold was 18.6 ± 7 ml/(kg·min) during test 1 and during test 2 it was 17.9 ± 7.3 ml/(kg·min); r = 0.91, p < 0.001. The corresponding values for maximal VO₂ were 30.4 ± 13 ml/(kg·min) and 31 ± 13 ml/(kg·min); r = 0.99, p < 0.001. It is concluded that this program offers a reproducible method of determining the lactate threshold during exercise testing employing a frequently used clinical protocol.