Circadian Rhythm… what is it and why does it matter?
Human physiology is organised around a daily cycle of activity and sleep, with the sleep:wake cycle being perhaps the most obvious of the 24 hour human circadian rhythm.
The circadian rhythm of the body is controlled by the suprachiasmatic nucleus (SCN); an internally generated clock entrained to external cues, known as zeitgebers, which can have a significant impact on optimising both sleep duration and sleep quality. The SCN is responsible for generating cyclic neuroendocrine mechanisms which promote wakefulness and sleepiness. Circadian rhythms alter throughout life stages: the circadian timing of an individual in their teenage years will be phase-delayed by around two hours in comparison to an individual in their fifties (Crowley et al., 2007). Throughout adolescence, the circadian clock continues to get later, reaching peak lateness in women at around 19 years of age, and men, around 21 years of age. Up until this age, individuals tend to want to get up later and go to bed later, therefore coaches of adolescent athletes should be mindful of scheduling training to work in harmony with the teenage body clock, rather than against it. Into early adulthood, the circadian clock moves to an earlier phasing. Awareness and recognition of these changes, along with subsequent adjustment of night time routines in conjunction with sleep drive, is key to the maintenance of appropriate sleep durations.
In 1976, a seminal piece of research by Horne and Ostberg used a self-assessment questionnaire to determine human chronotypes and identified that people did indeed have tendencies towards “morningness” or “eveningness”. More recently, Roenneberg et al. (2003) used a questionnaire to assess the sleep habits of 3000 participants and demonstrated a spectrum of chronotypes from
- those who favoured extreme early rising - “morning larks” - (sleep times 8pm-4am)
- to those favouring extreme late rising - “night owls” - (sleep times 4am-12pm).
This study demonstrated that light was the primary zeitgeber driving human circadian rhythms, which is further supported by more recent research (Youngstedt et al., 2019), and thus highlights the relevance of sleep hygiene education around light exposure pre-bedtime.
Roenneberg et al. (2003) concluded “extreme” morning larks were rare, as indeed were “extreme” night owls, and most people operate somewhere on a continuum between these two extremes.
Research has demonstrated differences between morning and evening types in terms of personality, mood and cognitive performance, and interestingly, females have been shown to have a greater predisposition towards morningness compared to males. Chronotype is determined by genetics, age, gender and environment. The key to maximising health is to work in harmony with your chronotype preference. The reduced morningness:eveningness questionnaire was developed in 1991 to quickly give a chronotype assessment, without the need for extensive questioning.
Answer these simple questions below to understand your chronotype:
- What time would you get up if you were entirely free to plan your day? Scoring:
- 5-6.59am – 5 points
- 7-7.59am – 4 points
- 8-9.30am – 3 points
- 9.31-10.59am – 2 points
- 11am-12pm – 1 point
- During the first half an hour of waking in the morning, how tired to do you feel? Scoring:
- Very tired – 1 point
- Fairly tired – 2 points
- Fairly refreshed – 3 points
- Very refreshed – 4 points
- At what time in the evening do you feel tired and ready for sleep? Scoring:
- 8-9pm – 5 points
- 9.01-10.14pm – 4 points
- 10.15pm -12.15am – 3 points
- 12.16- 1.59am – 2 points
- 2am onwards – 1 point
- At what point in the day do you think you reach your “feeling best” peak. Scoring:
- 12-5am – 1 point
- 5-8.30am – 5 points
- 8.31-10.30am – 4 points
- 10.31am-3.30pm – 3 points
- 3.31-8.30pm – 2 points
- 8.31pm-midnight – 1 point
- One hears about “morning” and” evening” types of people. Which one of these answers below do you consider yourself to be? Scoring:
- Definitely morning – 6 points
- Rather more a morning person than evening person – 4 points
- Rather more evening than morning person – 2 points
- Definitely evening – 0 points
Add up your scores from these 5 questions and use the following criteria to determine your chronotype:
- Definitely morning type – 22-25
- Moderate morning type – 18-21
- Neither – 12-17
- Moderate evening type – 8-11
- Definitely evening type – 4-7
Once you know your chronotype, aim to fit your lifestyle to match your physiological preference. Gaining an awareness of the times you function optimally can go a long way to enhance performance in both work and sports.