Which Cutoffs for Secondary V˙O2max Criteria Are Robust to Diurnal Variations?

The aim was to determine the minimum maximum oxygen uptake (V˙O2max) criteria cut-offs in highly trained athletes (i.e., maximum RER [RERmax], maximum HR [HRmax], maximum RPE [RPEmax], and maximum blood lactate concentration [BLmax]) necessary to determine maximum oxygen uptake (V˙O2max) during cardiopulmonary exercise tests (CPET), by balancing type I and type II errors. A further aim was to investigate if the defined cutoffs would be robust to diurnal and to day-to-day variations.

Data from two CPET studies involving young athletes were analyzed. In the first study, 70 male participants performed one CPET until exhaustion to define cutoffs. In the second study, eight males and five females performed one CPET on seven consecutive days at six different times of day (i.e., diurnal variation). The time of the CPET was identical on the sixth and seventh days (i.e., day-to-day variation). To ensure comparability both studies were carried out under the same conditions.

Participants' mean V˙O2max was 63.0 ± 5.3 mL·kg·min. RERmax ≥1.10 was reached by 100%, HRmax ≥95% of age-predicted HRmax by 99%, RPEmax ≥19 by 100%, and BLmax ≥8 mmol·L by 100% of participants, respectively. Regarding the intraday variations, latter cutoffs were not reached in two cases for RERmax and in one case for HRmax and BLmax. Intraclass correlations for the day-to-day variability were r = 0.823 for RERmax, r = 0.828 for HRmax, and r = 0.380 for BLmax, respectively.

The proposed high cut-off values for secondary criteria provide some assurance that V˙O2max may have been achieved in athletes without increasing type II errors. However, type I errors may still occur indicating that further methods such as V˙O2-plateau or V˙O2-validation may be required.