Whether you’re a morning person or love burning the midnight oil, we’re all controlled by “body clocks.” These body clocks (circadian rhythms) are inside almost every cell in the body and control when we feel awake and tired during a 24-hour period.
Our circadian rhythms are controlled by the brain’s suprachiasmatic nucleus, which detects light. When cells in your eyes register that it’s dark outside, they send these signals to the suprachiasmatic nucleus.
It then releases the hormone melatonin, which makes you feel tired. For morning larks, melatonin can rise around 6pm, making them feel tired by 9pm or 10pm. For night owls, melatonin can increase at 10pm/11pm or even later, meaning many aren’t tired until 2am or 3am.
Your chronotype is another factor that determines how your biological clocks affect your daily behaviour. For example early chronotypes (“morning larks”) rise early and are most active in the morning, but feel tired late in the afternoon or early evening. Late chronotypes (“night owls”) are tired during the morning, but feel awake in the evening.
Genetics can determine your body clock type, but it’s also largely influenced by schedule and lifestyle. It also changes over your lifetime.
People tend to be larks during the first 10 years of their life, then shift towards night owls during adolescence and early twenties. By the time you’re 60, you’ll probably have similar sleeping patterns as when you were 10.
Travelling across time zones also de-synchronises our body clocks, which need a chance to adjust. People who constantly change their sleeping patterns may experience “social jetlag”, which impairs performance.
The factors that determine your chronotype are unique. In a study to assess how the body clock affects peak performance (on both mental and physical tasks), 56 healthy individuals were asked to perform a series of cognitive tasks (to measure reaction time and their ability to plan and process information), and a physical task to measure their maximum grip strength.
The tests were completed at three different times between 8am and 8pm to see how an individual’s performance varied throughout the day.
Larks performed best earlier in the day (8am in cognitive tasks and 2pm in physical tasks). Night owls performed best at 8pm in both cognitive and physical tasks, and had better grip strength in the evening.
Larks performed their best in cognitive tasks immediately after waking up, and seven hours after waking up in the physical task. Night owls performed best in all tasks around 12 hours after waking up.
Compared to larks, night owls are significantly sleepier in the morning, making their reaction time slower by eight per cent. They’re also seven per cent weaker (using a maximum grip strength test) than morning larks.
Night owls also show a larger variation in peak performance throughout the day, suggesting they may be more sensitive to time-of-day changes than larks. For example, a night owl athlete competing against a morning lark at 8am would be more impaired than a lark competing against a night owl at 8pm. And because in athletics, success depends on the smallest margins, understanding precisely what time peak performance is likely could mean the difference between winning a gold medal or finishing in last place.
Knowing just how much our body clock affects us can also help us understand more about how we can gain maximum productivity in business or the best academic performance in school.
However, the typical structure of our society greatly favours morning larks over night owls. Since our typical working day doesn’t let night owls follow their preferred sleep and wake patterns, maybe it’s time we start thinking about being more flexible.
Dr Facer-Childs is a research fellow at the University of Birmingham in the United Kingdom