In competitive sports any substantial individual differences in diurnal variations in maximal performance are highly relevant. Previous studies have exclusively focused on how the time of day affects performance and disregarded the maximal individual diurnal variation of performance. Thus, the aims of this study were (1) to investigate the maximum diurnal variation in maximum oxygen uptake (VO2max), (2) to compare the diurnal variation of VO2max during the day to the day-to-day variation in VO2max, and (3) to investigate if there is a time-of-day effect on VO2max. Ten male and seven female athletes (mean VO2max: 58.2 ± 6.9 ml/kg/min) performed six maximal cardiopulmonary exercise tests including a verification-phase at six different times of the day (i.e., diurnal variation) and a seventh test at the same time the sixth test took place (i.e., day-to-day variation). The test times were 7:00, 10:00, 13:00, 16:00, 19:00, and 21:00. The order of exercise tests was the same for all participants to ensure sufficient recovery but the time of day of the first exercise test was randomized. We used paired t-tests to compare the nadir and peak of diurnal variations, day-to-day variations and the difference between diurnal and day-to-day variations. The mean difference in VO2max was 5.0 ± 1.9 ml/kg/min (95% CI: 4.1, 6.0) for the diurnal variation and 2.0 ± 1.0 ml/kg/min (95% CI: 1.5, 2.5) for the day-to-day variation. The diurnal variation was significantly higher than the day-to-day variation with a mean difference of 3.0 ± 2.1 ml/kg/min (95% CI: 1.9, 4.1). The linear mixed effects model revealed no significant differences in VO2max for any pairwise comparison between the different times of the day (all p > 0.11). This absence of a time-of-day effect is explained by the fact that peak VO2max was achieved at different times of the day by different athletes. The diurnal variations have meaningful implications for competitive sports and need to be considered by athletes. However, the results are also relevant to research. To increase signal-to-noise-ratio in intervention studies it is necessary to conduct cardiopulmonary exercise testing at the same time of the day for pre- and post-intervention exercise tests.

Purpose To determine age-dependent cutoff values for secondary exhaustion criteria for a general population free of exercise limiting chronic conditions; to describe the percentage of participants reaching commonly used exhaustion criteria during a cardiopulmonary exercise test (CPET); and to analyze their oxygen uptake at the respective criteria to quantify the impact of a given criterion on the respective oxygen uptake (V˙O2) values. Methods Data from the COmPLETE-Health Study were analyzed involving participants from 20 to 91 yr of age. All underwent a CPET to maximal voluntary exertion using a cycle ergometer. To determine new exhaustion criteria, based on maximal respiratory exchange ratio (RERmax) and age-predicted maximal HR (APMHR), one-sided lower tolerance intervals for the tests confirming V˙O2 plateau status were calculated using a confidence level of 95% and a coverage of 90%. Results A total of 274 men and 252 women participated in the study. Participants were nearly equally distributed across age decades from 20 to >80 yr. A V˙O2 plateau was present in 32%. There were only minor differences in secondary exhaustion criteria between participants exhibiting a V˙O2 plateau and participants not showing a V˙O2 plateau. New exhaustion criteria according to the tolerance intervals for the age group of 20 to 39 yr were: RERmax ≥ 1.13, APMHR210 − age ≥ 96%, and APMHR208 × 0.7 age ≥ 93%; for the age group of 40 to 59 yr: RERmax ≥ 1.10, APMHR210 − age ≥ 99%, and APMHR208 × 0.7 age ≥ 92%; and, for the age group of 60 to 69 yr: RERmax ≥ 1.06, APMHR210 − age ≥ 99%, and APMHR208 × 0.7 age ≥ 89%. Conclusions The proposed cutoff values for secondary criteria reduce the risk of underestimating V˙O2max. Lower values would increase false-positive results, assuming participants are exhausted although, in fact, they are not.

No abstract

We tested the hypothesis that participants with an oxygen uptake (normalV˙normalO2) plateau during incremental exercise exhibit a lower VO2‐deficit (VO2DEF)‐accumulation in the submaximal intensity domain due to faster ramp and square wave O2‐kinetics. Twenty‐six male participants performed a standard ramp test (increment: 30 W·min−1), a ramp test with an individualized ramp slope and a two‐step (moderate and severe) square wave exercise followed by a normalV˙normalO2max ‐verification bout. VO2DEF was calculated by the difference between individualized ramp test trueV˙O2 and trueV˙O2‐demand estimated from steady‐state trueV˙O2‐kinetics. Twenty‐four participants verified their trueV˙O2max in the verification test. Ten of them showed a plateau in the individualized ramp test. VO2DEF at the end of this ramp test (4.34 ± 0.60 vs 4.54 ± 0.43 L) was not different between the plateau and the non‐plateau group (P > 0.05). The plateau group had a significantly (P < 0.05) lower VO2DEF 2 minutes before termination of the individualized ramp test (2.24 ± 0.40 vs 2.78 ± 0.33 L). This coincided with a shorter mean response time (43 ± 9 vs 53 ± 7 seconds), a higher increase in trueV˙O2 per W (10.1 ± 0.2 vs 9.2 ± 0.5 mL·min−1·W−1) at the individualized ramp test as well as shorter time constants of moderate (36 ± 6 vs 48 ± 7 seconds) and severe (62 ± 9 vs 86 ± 10 seconds) square wave kinetics (all P < 0.05). We conclude that the trueV˙O2‐plateau occurrence requires a fast trueV˙O2‐kinetics and a low VO2DEF‐accumulation at intensities below trueV˙O2max.

Purpose 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. Methods 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. Results Participants’ mean V˙O2max was 63.0 ± 5.3 mL·kg−1·min−1. RERmax ≥1.10 was reached by 100%, HRmax ≥95% of age-predicted HRmax by 99%, RPEmax ≥19 by 100%, and BLmax ≥8 mmol·L−1 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. Conclusions 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.