Circadian rhythm directly influences muscle performance in Olympic swimmers

Joyce Chen ’23

Figure 1: Circadian rhythms influence daily physiological and biological functions. Because of this, Olympic swimmers have to be mindful of their swimming abilities throughout the day for optimal performance.

Organisms have a specialized inner clock known as the circadian rhythm, which is regulated by the Suprachiasmatic Nucleus (SCN) in the hypothalamus of the brain. Throughout the day, circadian rhythms in the body have direct control over physiological functions, including muscle strength and flexibility. Despite its relevance, there is a lack of research on the effects of circadian rhythms on Olympic athletes. The Olympic Games are tournaments held every four years, featuring elite athletes from all over the world. Due to its global nature, broadcasting on national television is tedious, as it requires the consideration of prime broadcasting times in other countries. Consequently, Olympians may have to perform at times that challenge their normal circadian rhythms. Researcher Dr. Lok and his team recruited Olympic swimmers to study the effects of the biological clock on physical performance. 

The team obtained data on Olympic finalist swimmers from the Games of Athens (2004), Beijing (2008), London (2012), and Rio de Janeiro (2016). They studied the influences of race type and time-of-day on performance by calculating and graphing each swimmer’s average swim time over race type, percent difference between race swim time, and the mean swim time for every stroke and length of performance. The data indicated that race type affected the Olympic swimmers’ speed. Possibly caused by levels of motivation, average speed in heat races was found to be slower than in the semifinals by 0.5%, and average speed in semifinals was about 0.2% slower than in the finals. In addition, swim performance appeared to be poorer earlier in the morning than in the late afternoon to early evening. This indicates that the time of day has a significant effect on physical performance. Moreover, previous research findings highlight how a variation in core body temperature (CBT) affects performance through passive warming of the muscles. CBT peaks in the early evening, therefore athletes will have improved performance within that time frame. However, athletes’ personal preferences for timing also play a role in this finding. If the athlete prefers early races, then he/she will tend to perform better in morning races than in evening races. 

The work of Dr. Lok and his team helps athletes learn how to improve their performance by understanding the role of circadian rhythm in physiological functions. Additional studies will extend into different kinds of athletes aside from swimmers.

Works Cited: 

[1] R. Lok, et al., Gold, silver or bronze: Circadian variation strongly affects performance in Olympic athletes. Sci Rep 10, (2020). Doi: 10.1038/s41598-020-72573-8

[2] Image retrieved from:


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