Determination of both the time constant of Vo2 and ΔVo2/ΔW from a single incremental exercise test:: validation and repeatability

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 (tau(V)over dot (O2)) and the amount of oxygen required at each load (Delta(V)over dot (O2)/DeltaW) 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 tau(V)over dot (O2), and interpolation of (V)over dot (O2) versus load to determine Delta(V)over dot (O2)/DeltaW. No significant differences were seen between the means of either tau(V)over dot (O2) or Delta(V)over dot (O2)/DeltaW determined with the two protocols. The correlation coefficient was 0.62 for for tau(V)over dot (O2) and 0.48 for Delta(V)over dot (O2)/DeltaW. The absolute differences (2 SD) were 11.6 s tau(V)over dot (O2) and 1.1 ml min(-1) W-1 for Delta(V)over dot (O2)/DeltaW. The equations were compared in the same steady-state test and good agreement of tau(V)over dot (O2) 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 tau(V)over dot (O2) and 1.2 ml min(-1) W-1 for Delta(V)over dot (O2)/DeltaW. In conclusion, tau(V)over dot (O2) and Delta(V)over dot (O2)/DeltaW 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 tau(V)over dot (O2) and Delta(V)over dot (O2)/DeltaW for evaluation of aerobic function.