Diurnal variation in gene expression and sports performance: a matter of timing?

Virtually all living organisms show oscillations in physiology that track the daily rhythm of light and darkness. In humans, not only the sleep-wake cycle has a period of about 24 hours, also basic physiological and cellular processes such as core-body temperature, cortisol levels or cell cycle and metabolism oscillate accordingly. While circadian oscillations are well studied at many levels from genes to behaviour, the impact of the molecular profile on the behavioural output has so far been hardly studied in humans. With the aim to establish a relation between genes and behaviour, we analysed time series data sets of gene expression and sports performance from the same human subjects. Gene expression of two specific core-clock genes, measured via RT-PCR, shows circadian variation in samples of bodily fluids, which constitutes a practical source for human genetic material. Sports performance was evaluated by a set of three standardized tests probing strength and endurance. While we find overall best sports performance in the afternoon, the individual best performance times, which show larger variations, can be predicted by a machine learning approach. Besides best performance time, the variance in sports performance over the day is of interest. Here we discuss our latest findings in the field and their putative benefit for professional athletes, as well as their general implications for our well-being.