Physiology Friday #113: Time of Day Affects Peak Athletic Performance

A study of multiple Olympic Games reveals that athletes' performances are highly dependent on the time of day, an effect likely due to circadian variations in physiology from morning to night.

Hello friends,

Happy Physiology Friday!

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Circadian rhythms are a topic I've blogged about extensively and one I find very interesting. Basically, circadian rhythms are internal oscillating "clocks" that we have present throughout our body, controlling the time of day variations in things like body temperature, hormone release, motivation, and metabolism.

One area of research where circadian rhythms have gained attention is sport performance. This is because like all other functions, physical performance also shows a time of day variation. Everything from oxygen consumption, muscle contraction, speed, and peak power output have been shown to depend on time of day.

Why is this important? Well, if you're an athlete in competition, competing at the "right" time of day is important to maximize performance. Even if you're not competing for a place on the podium, selecting the optimal time of day to train could help one maximize training output and adaptation. 

For Olympic athletes, the time when a race occurs could be the difference between winning a medal or getting fourth place. In addition, athletes in the games are often competing in odd time zones and required to compete at different times of the day.

While one might think that Olympic athletes would be "robust" to circadian performance variation and be able to compete at their best morning 'til night, nobody has studied whether these elite competitors also exhibit time-of-day performance variation.

Today's study aimed to do just that -- determine if Olympic athletes exhibited time of day variation in their performance, and if so, by how much.

Researchers analyzed swimming data from the Olympic games in Athens, Beijing, London, and Rio de Janeiro. Why swimming? This sport is under less influence from external variables like shoes, equipment, and environmental factors and was therefore proposed to be the best way to independently study effect of time of day.
 

Results

Time of day significantly influenced performance. 

The data indicated that swim performance was worse in the early morning (5:12 a.m) and best in the late afternoon (5:12 p.m.) for both males and females.

The overall magnitude of this difference wasn't meager -- the difference in performance between morning and evening was 0.37%. This time/performance difference for time of day was actually greater than the time difference separating the gold and silver medals in 40% of the finals, silver and bronze medals in 64% of the finals, and bronze and fourth place in 61% of the finals.

Thoughts and musings

There are quite a few important implications from these findings. 

First -- they tell us that even though Olympic athletes represent the "elite of the elite" in terms of sport performance, they are still under the influence of endogenous circadian rhythms. This means that despite elaborate design of training, diet, and sleep, not every aspect of performance can be totally controlled.

However, the results can also inform training strategy. Studies have shown that the time of day when you train can "train" your circadian rhythms to perform better at that time of day. I.e. if you always train in the morning, you can offset some of the morning attenuation in performance relative to the evening.

What is responsible for this time of day effect?

Core body temperature explains a lot -- higher body temperature in the afternoon means warmer muscles and better performance. 

This variation has also shown to be influenced by your "chronotype" -- whether you're a morning or evening person. Morning types are likely to perform better in the morning, and vice-verse for evening types. While this study didn't assess for athlete chronotype (they had no way to do so...), it would have been interesting to see. 

If you're "forced" to compete at your suboptimal time of day, this could make a huge difference. 

Luckily, most of us have control over when we choose to train, and can craft our training regimens to optimize performance and benefits. We can also align training with our peak motivation -- also very important for exercise adherence. Obviously, hectic schedules can dictate when we're able to train, so it's not always 100% within our control -- just like with Olympic athletes. 

For me, morning training is preferred, though I often train twice per day. I DO notice improved power, mood, and energy in the afternoon, which aligns with data from this and other studies. 

What about you? I'd love to hear when you like to train and why in the comments below!

Until next Friday,

~Brady~

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Study cited
Lok R, Zerbini G, Gordijn MCM, Beersma DGM, Hut RA. Gold, silver or bronze: circadian variation strongly affects performance in Olympic athletes. Sci Rep. 2020;10(1):16088.