Marathon race performance: lark or owl for the win?

For maximum exercise performance, it stands to reason that all the physiological systems in the body must be working optimally and in harmony. However, there are many biological rhythms woven into human physiology that also play a role in determining performance. Some are quite short duration such as alertness and attention cycles, which repeat every hour or two, and some are much longer – for example the menstrual cycle in women, which repeats each month.

Of these, the daily night/day ‘circadian’ rhythm – governed by the light-dark cycle which occurs every 24 hours - 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 through the day (see figure 1, which shows the typical daily variations of melatonin, secretion, core temperature, triacylglycerol, alertness and reaction time as a result of the circadian rhythm)⁽¹⁾.

Figure 1: Typical circadian rhythm-induced fluctuations in the body