Circadian rhythms are 24-hour internal clocks that are essential for our bodies to function well. Ticking in the background, our circadian rhythm influences psychological and physiological performances throughout the day, although it’s most commonly known to align our sleep cycle. When this clock is “out of whack,” you’ll likely feel it.
In a University of Groningen-funded study published in Scientific Reports, Renske Lok and her team of researchers looked to understand how the time-of-day and circadian effects can optimize sports performance. Using Olympic swim times from 2004 to 2016, Lok and her team found clear time-of-day effects on Olympic athletes’ physical performance.
Circadian rhythms affect muscle strength, muscle flexibility, grip strength, limb movement speed, and the perceptual and cognitive aspects of athletic performance. However, Lok and her team acknowledge that other factors may also affect this relation, such as core-body temperature (CBT), oxygen uptake, melatonin release, type of exercise, and psychological considerations, among others.
Regardless, the study’s purpose was to determine if Olympic athletes are affected by circadian fluctuations in physical performance. Olympic athletes are often required to perform at different times of the day while adjusting to different time zones. For their study, Lok and her team analyzed Olympic swim data from the Games of Athens (2004), Beijing (2008), London (2012), and Rio de Janeiro (2016).
Compared to other sports, swimming requires minimal aiding equipment that could increase variation between participants, such as shoes, and uses the regulated water temperature in Olympic pools. Lok and her team reasoned that Olympic swim performance might reflect a clear generalization of the daily variation in physical performance.
For the study, Lok and her team included data of 144 athletes who made it to the finals, recording individual swim times over race type (heat, semi-finals, finals), for each stroke (backstroke, butterfly, etc.), distance, and Olympic venue. The study found that race type significantly affected swim performance. Athletes performed slowest in heats, faster in semi-finals, and most quickly in finals. This can likely be attributed to psychological motivation.
However, performance differences between race types also varied between Olympic venue locations. The percentage difference between heats and finals in Beijing was much smaller than in the Athens and London Olympic venues. To understand their findings, Lok and her team turned to possible time-of-day effects.
After plotting all 1722 data points into a sine fitted model, Lok and her team discovered that swim performance was worst in the early morning (5 a.m.) and best in late afternoon (5 p.m.). There was no significant difference between sexes.
In 40 per cent of the finals, the time-of-day had a more significant effect than the time differences between gold or silver medal finishing times. Time-of-day also exceeded the time differences between silver and bronze in 64 per cent of the finals, and the time difference between bronze and fourth place in 61 per cent of the finals.
Lok and her team demonstrate that, despite following training schedules from sun-up to sun-down, time-of-day still affects professional athletes’ performance. The study concluded that time-of-day, the indicator of our circadian rhythms, affects physical performance.
Of course, we also have our individual chronotype to consider. Chronotypes describe an individual’s biological optimal timing for activity and sleep. According to Lok and her team, early chronotypes perform best around mid-day, intermediate chronotypes around mid-afternoon, and late chronotypes in the evening.
Lok and her team note that a selection bias toward earlier chronotypes can exist. For example, swim training times are often scheduled in the early morning. Later chronotypes may also have more daytime variation in performance, threatening their selection for the Olympics in favour of early chronotypes.
Based on these findings, Lok and her team suggest that optimal physical performance might depend on several factors: a combination of mental performance, time awake, and circadian rhythm in muscle cells, among others. In the upcoming Olympics, Lok suggests athletes may need to perform at times of day that do not coincide with their circadian peak performance. With this foresight, athletes may consider adjusting their circadian system to ensure they give it their best when it’s time to win a medal.
In a University of Groningen-funded study published in Scientific Reports, Renske Lok and her team of researchers looked to understand how the time-of-day and circadian effects can optimize sports performance. Using Olympic swim times from 2004 to 2016, Lok and her team found clear time-of-day effects on Olympic athletes’ physical performance.
Circadian rhythms affect muscle strength, muscle flexibility, grip strength, limb movement speed, and the perceptual and cognitive aspects of athletic performance. However, Lok and her team acknowledge that other factors may also affect this relation, such as core-body temperature (CBT), oxygen uptake, melatonin release, type of exercise, and psychological considerations, among others.
Regardless, the study’s purpose was to determine if Olympic athletes are affected by circadian fluctuations in physical performance. Olympic athletes are often required to perform at different times of the day while adjusting to different time zones. For their study, Lok and her team analyzed Olympic swim data from the Games of Athens (2004), Beijing (2008), London (2012), and Rio de Janeiro (2016).
Compared to other sports, swimming requires minimal aiding equipment that could increase variation between participants, such as shoes, and uses the regulated water temperature in Olympic pools. Lok and her team reasoned that Olympic swim performance might reflect a clear generalization of the daily variation in physical performance.
For the study, Lok and her team included data of 144 athletes who made it to the finals, recording individual swim times over race type (heat, semi-finals, finals), for each stroke (backstroke, butterfly, etc.), distance, and Olympic venue. The study found that race type significantly affected swim performance. Athletes performed slowest in heats, faster in semi-finals, and most quickly in finals. This can likely be attributed to psychological motivation.
However, performance differences between race types also varied between Olympic venue locations. The percentage difference between heats and finals in Beijing was much smaller than in the Athens and London Olympic venues. To understand their findings, Lok and her team turned to possible time-of-day effects.
After plotting all 1722 data points into a sine fitted model, Lok and her team discovered that swim performance was worst in the early morning (5 a.m.) and best in late afternoon (5 p.m.). There was no significant difference between sexes.
In 40 per cent of the finals, the time-of-day had a more significant effect than the time differences between gold or silver medal finishing times. Time-of-day also exceeded the time differences between silver and bronze in 64 per cent of the finals, and the time difference between bronze and fourth place in 61 per cent of the finals.
Lok and her team demonstrate that, despite following training schedules from sun-up to sun-down, time-of-day still affects professional athletes’ performance. The study concluded that time-of-day, the indicator of our circadian rhythms, affects physical performance.
Of course, we also have our individual chronotype to consider. Chronotypes describe an individual’s biological optimal timing for activity and sleep. According to Lok and her team, early chronotypes perform best around mid-day, intermediate chronotypes around mid-afternoon, and late chronotypes in the evening.
Lok and her team note that a selection bias toward earlier chronotypes can exist. For example, swim training times are often scheduled in the early morning. Later chronotypes may also have more daytime variation in performance, threatening their selection for the Olympics in favour of early chronotypes.
Based on these findings, Lok and her team suggest that optimal physical performance might depend on several factors: a combination of mental performance, time awake, and circadian rhythm in muscle cells, among others. In the upcoming Olympics, Lok suggests athletes may need to perform at times of day that do not coincide with their circadian peak performance. With this foresight, athletes may consider adjusting their circadian system to ensure they give it their best when it’s time to win a medal.
