Study: Time of Day ‘Strongly Affects’ Performance of Olympic Swimmers

Photo Courtesy: Annie Grevers

A study by a Stanford postdoctoral fellow published last week finds that Olympic swimmers are more than a third of a second faster, on average, in the evening than in the morning.

The study is titled, “Gold, silver or bronze: circadian variation strongly affects performance in Olympic athletes.” It was performed by Renske Lok, Ph.D., a psychiatry fellow who studies circadian biology at Stanford, during her time at the University of Groningen in the Netherlands. Her research was published in the journal Scientific Reports.

Lok analyzed the times of 144 swimmers (72 men, 72 women) in the finals of the Athens, Beijing, London and Rio Olympics, choosing swimming because of the limited variables affecting performance and normalizing the data based on race type (heat, semifinal, final). The analysis of those swims concluded that times were slower in the morning and faster in the afternoon, by an average of 0.39 seconds. The best results for Olympic swimmers came around 5 p.m. local time.

From the paper’s abstract:

Performance was strongly affected by time-of-day, showing fastest swim times in the late afternoon around 17:12 h, indicating 0.32% improved performance relative to 08:00 h. This study reveals clear effects of time-of-day on physical performance in Olympic athletes. The time-of-day effect is large, and exceeds the time difference between gold and silver medal in 40%, silver and bronze medal in 64%, and bronze or no medal in 61% of the finals.

“The magnitude of the effect is pretty big,” Lok said. “The difference was amazing, considering that athletes train at all times of the day.”

Given her background, Lok focused on circadian effects as a cause. Biological factors like body temperature, blood glucose, oxygen saturation levels and various hormone (insulin, cortisol, testosterone, etc.) levels have regular peaks according to our internal body clock, which affect when people hit peaks and troughs in their physical and mental functioning. People’s tendencies in this area, their chronotype – defined in the paper as “describing an individual’s biological optimal timing for activity and sleep” – roughly hew to what we think of as early birds (or larks) and night owls.

The research has practical applications. While chronotype is a relatively stable trait, athletes can adjust their sleep and meal schedules over shorter periods to optimize training and performance. It’s especially important in an Olympic or World Championships setting, where the timing of finals isn’t determined for the good of athletic performance but to maximize TV visibility. Those differences in timing, such as the morning finals and evening prelims at the Beijing Olympics that will recur at the 2021 Tokyo Games, provided Lok with variables to study.

The full paper is available to read here.

1 comment

  1. avatar

    Thanks Mathew- a good read.

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