In Athletes, the Diurnal Variations in Maximum Oxygen Uptake Are More Than Twice as Large as the Day-to-Day Variations

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.

Transcriptomic, proteomic and phosphoproteomic underpinnings of daily exercise performance and Zeitgeber activity of endurance training

“…Moreover, insulin sensitivity, mitochondrial respiration, glucose, and lipid-related metabolites likewise follow similar patterns in muscle tissue (Dyar et al, 2018;Loizides-Mangold et al, 2017;Sato et al, 2018). In line with this, daily variations in resistance and endurance exercise peak performance have been reported during the normal active phase in humans (Mirizio et al, 2020) and rodents (Ezagouri et al, 2019) in some, but not all trials (Knaier et al, 2019;Mirizio et al, 2020). The robustness and timing of such performance peaks seems highly variable, depending on a multitude of parameters including chronotype, time from awakening, muscle and liver glycogen levels, nutritional status, and temperature (Facer-Childs 5 and Brandstaetter, 2015; Hearris et al, 2018).…”

Effect of intensive prior exercise on muscle fiber activation, oxygen uptake kinetics, and oxygen uptake plateau occurrence

“…The pedalling rate during the tests was set at 80 rpm, and the temperature was kept constant at 20 °C by air condition. To avoid potential effects of diurnal variation on (Knaier et al 2019a ), all tests were performed at the same time of day (± 1 h).…”

“… , maximal carbon dioxide production ( ), and maximal respiratory exchange ratio (RER max ) were calculated as the mean of the final 30 s of the ramp and verification test. Based on the test–retest reliability of (Katch et al 1990; Knaier et al 2019a ), participants with a in the verification bout more than 5% higher compared to the unprimed ramp test were excluded from the subsequent analyses. The -plateau was determined from the slope of the –workload-relationship of the final 50 W ( ) using linear regression analyses.…”

Verification-phase tests show low reliability and add little value in determining V̇O2max in young trained adults

“…He/she would therefore be excluded, although he/she might have reached the inclusion criteria if randomized to another time of the day for the first test session. Therefore, we reduced the criterion for by 10% which is based on the expected maximum diurnal variation of during the day [ 22 ]. On the first test day, participants were physically examined by a physician; 12 channel resting electrocardiography was performed and medical history was assessed.…”

“…Furthermore, CPET's are often performed at different times of day. Therefore, criteria for the diagnosis of must be robust against diurnal variations [ 22 ]. However, the diurnal variability of the -plateau and the verification procedure is unclear.…”