Abstract
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.
Highlights
In competitive sports any substantial individual differences in diurnal variations in maximal performance are highly relevant
Because it may be possible that a participant performs his/her first cardiopulmonary exercise test (CPET) at the nadir of performance, we reduced the criterion for maximum oxygen uptake (VO2max) by 10% based on the expected maximum diurnal variation of VO2max during the day
Twenty-seven participants were assessed for eligibility, whereby six participants did not meet the inclusion criteria for VO2max
Summary
In competitive sports any substantial individual differences in diurnal variations in maximal performance are highly relevant. The main issue is that most studies measured performance only at two times of the day (Reilly and Baxter, 1983; Hill et al, 1988; Burgoon et al, 1992; Reilly and Garrett, 1998; Atkinson et al, 2005; Brown et al, 2008; Chtourou et al, 2012; Souissi et al, 2012; Hill, 2014; Rae et al, 2015; Aloui et al, 2017) with 07:00 and 17:00 being the most frequently used times Such a large measurement interval carries a high risk of missing the peak and nadir of performance during the day. The measurement of maximum oxygen uptake (VO2max) in a cardiopulmonary exercise test (CPET), which is supposed to represent the gold standard to determine aerobic performance, was only measured in studies with a small sample size (Deschenes et al, 1998) or with large measurement
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
