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LOGINChronobiology: Rhythms and Athletic Injury
We may live in a high-tech 24/7 world, but fundamental biological rhythms remain deeply ingrained in our physiological makeup. Andrew Hamilton explains how these rhythms can affect injury risk, and the implications of this for coaches and clinicians.
Humans have evolved in and are surrounded by a world full of rhythms. It would be incredible therefore if these rhythms didn’t exert a significant effect on our physiological function and performance potential, and in recent years, the field of ‘chronobiology’ has confirmed this is indeed the case.
You will no doubt be well aware of the powerful circadian (daily) rhythm. This is the most fundamental biological rhythm, regulating our sleeping and waking patterns. However, other rhythms can also impact physiological function, although the magnitudes of their effects tend to be somewhat weaker (which can make some of them rather difficult to detect against the background of environmentally induced physiological variations).
Table 1: Summary of biological rhythms.
| Rhythm | Length | Strength | Description and Examples |
|---|---|---|---|
| Ultradian | Less than 24 hours | Weak | Weaker, short-term rhythms such as 90-minute attention and alertness cycles, brain wave activity cycles, REM and non-REM phases of sleep etc. |
| Circadian | Around a day | Strong | The normal wake/sleep cycle associated with day and night; daily variations of blood pressure and temperature |
| Circatrigintan | Varies, but averages around 29-30 days | Strong | The menstrual cycle in women |
| Circannual | Around a year | Weak, but may be stronger in some individuals | Seasonal affective depression, increased risk of winter illness |
Circadian Rhythm
The circadian rhythm is the most powerful rhythm affecting humans; as well as the sleep/waking cycle, it affects hormone secretions, body temperature, mental alertness and physical performance capacity. The graphs below in figure 1 show the typical daily variations of the hormone melatonin, core temperature, levels of triacylglycerol, alertness and reaction time as a result of the circadian rhythm(1).
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