Biological Clocks And Olympic Performance

Many elements go into a successful high-level athletic performance. Training, mental preparation and nutrition are key aspects of winning performance. But what about an athlete’s biological clock? Are certain physiological characteristics peaking at different times of day? If so, what would it mean for athletic performance?

A group of chronobiologists at the University of Groningen asked some of these same questions. They studied swimmers in four different Olympic Games to see if variations in time of day for heats, semi-finals and finals made a difference in the performance of the athletes and affected the outcomes.

Their conclusion is that an athlete’s biological clock has a sizeable affect on their performance. They believe that shifting this clock to help achieve peak performance at just the right time can mean the difference between victory and a near-miss. They published their findings in the journal Scientific Reports.


“In many sports, the differences between coming first or second, or winning no medal at all, are very small,” explains Renske Lok, first author of the paper and former PhD student at the University of Groningen. “We wondered whether an athlete’s biological clock was playing a role.”

This clock determines our bodies’ daily rhythms. It regulates key physiological characteristics such as blood glucose levels and core body temperature.”And we know that peak performance usually coincides with the peak in core body temperature,” says Lok.

Her investigation of this concept was centered around analyzing the times of Olympic swimmers who reached the finals for their particular stroke and distance.


“This meant that they had to swim three rounds: the heats, the semi-finals and the finals.” The study used data drawn from websites listing the official times and results for four Olympic Games: Athens (2004,) Beijing (2008,) London (2012,) and Rio de Janeiro (2016.)

“We chose swimming because the external situation is very similar: the water temperature is well-regulated and hardly any equipment is used.” The results for each participant were normalized to account for factors specific to any one Games, such as the shark-skin competition suits worn in the Beijing Games. They calculated the mean individual time across three rounds, then compared each round to the average.

The researchers came to two interesting conclusions. “First, athletes performed best in the finals, while the heats were always slower than the semi-finals. They were able to adapt their performance and save their best efforts for the finals.”


The second, and perhaps more interesting, finding was that the difference between semi-finals and heats was smallest in Beijing. “This was very interesting since in the other venues, heats were scheduled in the morning, while semi-finals and finals took place in the evening. In Beijing though, the heats were scheduled in the evening, while semi-finals and finals were in the morning and in the afternoon.”

This correlated with the idea that the time of day affected performance in the heats, semi-finals and finals. So Lok and her team eliminated all the variations that weren’t connected to the athletes’ biological clock. The result was a clear sinusoid performance curve through the course of the day.

“The performance was not so good in the morning, better in the afternoon and worse again in the late evening.” Their findings predicted that the fastest times should be swum just after five o’clock in the afternoon.


The amplitude of the effect, as represented by the degree of sinusoid function, was significant. In the finals, it meant the time difference between a bronze medal and none in 61 percent of the races, between silver and bronze in 64 percent of races and between gold and silver in 40 percent of the races.

It may be tempting to dismiss this by noting that all swimmers are in the pool in the finals. “Yet not all swimmers will have the same chronotype,” says Lok.

Not all swimmers are at peak performance at the same times of day. The impact of this variance could mean the difference between a medal and none at all. Lok thinks athletes may be able to use this to gain an advantage.


“It is possible to shift your biological clock by exposing yourself to extra daylight at the right time of day. If you do this over the course of several days, you could shift the time of peak performance towards the time of a race.”

Is this advantage transferable to other sports? Maybe, maybe not. ‘In cycling, for example, the quality of the bike is also important,’ says Lok, who is now a postdoctoral researcher at Stanford University’s Department of Psychiatry and Behavioral Sciences.

For this study, the focus was on the biological clock influencing arm and leg muscles. Based on this, translation to other sports seems plausible. “Furthermore, these elite athletes train all day, and we have shown that this does not overrule the effect of the circadian rhythm.”


Training, nutrition, mental preparedness, rest and recovery have always been keystones in the foundation of building elite athletes. Is it time that we consider the athlete’s biological clock? Can that clock be shifted from it’s natural rhythm to one that syncs up with the time of competition?

If so, that may just be the difference between victory and defeat for the otherwise perfectly tuned athletic machine.

Keep the faith and keep after it!

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Journal Reference – R. Lok, G. Zerbini, M. C. M. Gordijn, D. G. M. Beersma, R. A. Hut. Gold, silver or bronze: circadian variation strongly affects performance in Olympic athletes. Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-72573-8

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