Determination of both the time constant of V̇O: validation and repeatability2: validation and repeatability and ΔV̇O: validation and repeatability2: validation and repeatability/Δ: validation and repeatabilityW: validation and repeatability from a single incremental exercise test: validation and repeatability

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A single incremental cycle exercise test including a steady-state load, combined with respiratory gas exchange, was performed with the objective of determining the time constant (τV̇O2) and the amount of oxygen required at each load (ΔV̇O2/ΔW) by using a novel equation. The protocol was validated using four exercise tests at different constant loads and conventionally fitted mono-exponential functions to determine τV̇O2, and interpolation of V̇O2 versus load to determine ΔV̇O2/ΔW. No significant differences were seen between the means of either τV̇O2 or ΔV̇O2/ΔW determined with the two protocols. The correlation coefficient was 0·62 for τV̇O2 and 0·48 for ΔV̇O2/ΔW. The absolute differences (2 SD) were 11·6 s for τV̇O2 and 1·1 ml min−1 W−1 for ΔV̇O2/ΔW. The equations were compared in the same steady-state test and good agreement of τV̇O2 was obtained (R = 0·99). The 5–6-week repeatability (incremental test) was evaluated. No statistical differences were seen between the mean of the repeated tests. The difference between the tests (2 SD) were 20 s for τV̇O2 and 1·2 ml min−1 W−1 for ΔV̇O2/ΔW. In conclusion, τV̇O2 and ΔV̇O2/ΔW can be determined from a single incremental test. The validation showed an acceptable agreement, although the variations in absolute values were not negligible. This could partly be explained by the natural day-to-day variation and fluctuations in incoming raw data. The test–retest variation in absolute values was considerable, which must be taken into account when using τV̇O2 and ΔV̇O2/ΔW for evaluation of aerobic function.

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