Abstract

Background: τV˙o₂ at the onset of constant work rate (CWR) exercise is a variable of aerobic fitness that shortens with physical training and lengthens with cardiopulmonary disease. Determination of τV˙o₂ with sufficiently high confidence has typically required multiple exercise transitions limiting its clinical application.

Objectives: To design a protocol to determine τV˙o₂ reliably but simply.

Methods: On each of three days, five healthy men performed two CWR tests on a cycle ergometer below the metabolic threshold (V˙o₂θ) for blood lactate accumulation as determined by gas exchange measurements followed by an incremental work rate (IWR) test. τV˙o₂ was determined (a) from the on-transit (on-τV˙o₂) and off-transit (off-τV˙o₂) of six CWR tests both individually and superimposed, using non-linear regression with a monoexponential model, and (b) by geometric analysis of the IWR tests (ramp-τV˙o₂).

Results: Group means (SD) were: V˙o₂max 3.84 (0.44) litres/min, V˙o₂θ 1.88 (0.23) litres/min, steady state exercise V˙o₂ 1.67 (0.07) litres/min, on-τV˙o₂ 38.0 (5.3) seconds, off-τV˙o₂ 39.0 (4.3) seconds, and ramp-τV˙o₂ 60.8 (15.4) seconds. On-τV˙o₂ correlated with off-τV˙o₂ (r  =  0.87), V˙o₂max (r  =  −0.73), and V˙o₂θ (r  =  0.89). The pooled mean τV˙o₂ from six superimposed tests agreed with the arithmetic grand mean of the six tests.

Conclusions: The average of on-τV˙o₂ and off-τV˙o₂ fell within the 95% confidence interval of the pooled mean by the second test. Ramp-τV˙o₂ was longer and less reproducible. These findings support the use of both on- and off-transit data for the determination of τV˙o₂, an approach that reduces the number of transitions necessary for accurate determination of τV˙o₂, potentially enhancing its clinical application.