Biological rhythms in sport

Biological rhythms are characteristic of all living things, recurring either at very short intervals (a few milliseconds) or at relatively longer ones (24-hour cycles, menstrual cycles, etc.). For example, over the course of a day body temperature fluctuates by 0.4-0.5 degrees, reaching its lowest at about 4 a.m. and its highest at 6 p.m. Resting heart rate also varies by 5-15% over a day, peaking at around 3 p.m. The hormonal changes across the day are very well known. A person’s height varies by roughly 1.1% over a day: we are tallest at 8 a.m. and shortest around midnight.

When are the best athletic results achieved?

World records are set mainly in the late afternoon and evening, between 17 and 23 hours, when body temperature is at its highest. This is especially pronounced in sports that demand speed and strength.

Studies have shown that muscle strength and contraction speed are better in the late afternoon. In isometric contractions, strength peaks between 14 and 19 hours, varying by up to 6% over a day. A two-peak response has also been found, once before noon and once in the late afternoon. Back muscle strength is likewise greater in the late afternoon.

Interesting results have also come from research into the biological rhythm of jumping ability. Here too, the best results are achieved in the late afternoon.

A few studies on strength training have also shown that gains in isotonic strength are greater when you train in the late afternoon. The likely reason is that people who train in the late afternoon have higher blood concentrations of growth hormone (somatotropin) and testosterone. On the other hand, it has been shown that morning training times generally suit learning technique better. Even so, injuries are less common among those who exercise in the late afternoon. To some extent, it also matters whether the athlete is a morning or an evening type. A whole range of physiological indicators are not tied to this kind of biological rhythm, such as heart rate and oxygen consumption. Still, researchers have obtained very varied results here. The rule, however, is that the better trained the athlete, the more clearly this rhythmicity shows.

In summary, it is generally most beneficial to train and compete between the hours of 16 and 20, based on the athlete’s body clock time, which after traveling west may mean the early morning hours.

Author: Toivo Jürimäe (professor)

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