Circadian Rhythm & Exercise: What is the Link

Circadian rhythm is essentially your body clock. You often hear the term body clock used to refer to your ability to sense what time it is and even wake up on time without an alarm but it is so much more than this! Your body clock determines things like sleep, appetite, digestion, hormonal secretion and body temperature.

The word ‘circadian’ refers to a set of biological processes occurring on a 24 hour cycle. Your circadian rhythm is controlled by small nuclei in the middle of your brain called the suprachiasmatic nuclei (SCN). These are influenced by light fluctuations but occur even in their absence. ‘Rhythm’ simply refers to the timing of these biological processes. So, your circadian rhythm is your body’s 24-hour biological routine!

Your natural circadian rhythm determines your energy levels – when you feel sleepy and when you feel alert. It is affected by both lifestyle and genetics.

Circadian rhythm disorders are a thing and occur when your natural body clock is out of sync. They can be caused by hormone imbalances as well as genetic conditions that affect hormone secretion. Healing this depends on what is causing it and it is recommended that you consult with your GP and potentially a sleep specialist if sleep problems are affecting your quality of life. Symptoms of a circadian rhythm disorder include extreme daytime sleepiness, brain-fog, and significant emotional dysregulation due to exhaustion.

Blue light – There is fascinating research that has found that blue light can have a drastic effect on your circadian rhythm and quality of sleep. Blue light isn’t just light that looks blue. It is also white light that has the wavelengths of blue light in it. To reduce the impact of blue light, minimise blue/white light from when the sun is setting until it is coming up again, or for as long as you want to sleep. Use very warm or red light in the evenings and cover any light coming from electrical items with electrical tape. Consider blue-light filter glasses or if you wear glasses already, having lenses with a blue-light filter in them. You can even buy special light bulbs for this purpose or even use candles. You can find out more about how the colour of light affects you here.

Changing time zones – jet lag is a symptom of a disrupted circadian rhythm.

Changes in certain genes – Genes can mutate due to ‘errors’ in DNA replication during cell division. Also, it is proven that both age, lifestyle, and environment, as well as significant life experiences have the power to change the way our genes work without changing the genetic code itself. This field of research is called epigenetics.

You can reset your circadian rhythm by monitoring the above disruptors as best you can. Try to sleep and wake at regular times. Practice sleep hygiene with a solid evening routine. In fact, sleep experts say that your entire day is setting you up for how you sleep! Know that everything you do and everything your body registers from your environment is sending signals to your brain.

Practice a morning routine that eases you into your day and helps to regulate your nervous system. Your morning routine sets you up for the kind of day you will have. If you want to feel grounded, calm and focused throughout your day, make sure the first things you do in the morning put you in that headspace. The same applies for your evening routine. If you want to feel restful and ready to close the day, create an evening routine that does that for you. Many people report a very busy mind when they are trying to sleep. Preparing for sleep aids this. If a busy mind is keeping you up at night, you can try this evening routine: 

A brain dump/ stream of consciousness to get it all out

A shower or bath to ‘wash the day off’ 

Some unstimulating activity such as an evening meditation or listening to a relaxed podcast. Minimise screens (and blue light) as much as possible.

You can also use exercise to shift your circadian rhythm. The relationship between the two goes both ways. Below you will find out more about this.

The link between circadian rhythm and exercise

You can use exercise to regulate your circadian rhythm too.

Your muscles have a circadian rhythm of their own within your wider circadian rhythm. It is called a ‘skeletal muscle clock’. Their main purpose is to regulate physiological cycles (that are part of your circadian rhythm) in response to physical changes in and around your muscles – in other words, physical activity and environmental changes.

This means exercise can reset your circadian clock. Your brain is expecting to move less at night – when it is dark – than in the day. So you can use exercise to signal to the body when it should be awake and when it should be resting. Exercise in the morning to communicate to your brain “it is time to be alert” and reduce movement in the evening to show your brain “it is time to rest”. Exercising earlier in the day is associated with earlier bed and wake times, too! So if you’re trying to become a morning person, this is highly recommended. I have personally seen clients become morning persons simply because the only time we could fit in their sessions was before work and they adapted accordingly and came to love their mornings.

To maximise the effect of your workout on your circadian rhythm exercise outside. Your body can sense the light outside and therefore what time of day it is. Exercising outside has a host of other health benefits and you can find out more about them here.

How you can make circadian rhythm a part of your exercise routine

If you have the flexibility and desire to exercise in accordance with your circadian rhythm, here is how you can do it. Research shows that due to circadian rhythm, you are at peak physical performance in the later afternoon – between 2 and 6pm. Your body temperature is high and so also is metabolic function, flexibility and speed. This isn’t possible for most people who have busy schedules and need to get their workouts done at the very start or end of the day. 

Note it isn’t good to exercise at night right before sleep. If the end of the day (or within 3 hours of your bedtime) is the only time you can fit in a workout, consider something low intensity like yoga or walking. This is because increasing your heart rate and core body temperature makes it hard to fall asleep. Your core body temperature in particular takes some time to re-regulate.

Remember that when it comes down to it, consistency is the most important consideration in choosing when to exercise. There are two key reasons for this. One is that in terms of your circadian rhythm, exercising at a regular time means that your body knows what to expect and can factor it into its 24-hour rhythm. The second is that exercising at the same time everyday helps make it a habit. Habits allow us to accomplish things with minimal effort because a lot of it is done on autopilot. This means you can be consistent for long lengths of time.

Note whether you are a morning person or evening person. If you struggle to sleep early and find yourself most productive at night, an evening workout might make sense for you. On the contrary, if you are like me and enjoy sleeping and waking early, a morning workout probably makes the most sense for you.

Key Takeaways

• Exercise and circadian rhythms are closely linked
• We are at our peak athletic performance in the afternoon, but that doesn’t necessarily mean that’s the best time for YOU to workout
• You can consider your circadian rhythm – when you have the most energy – when choosing a regular time to workout 
• Not only does your circadian rhythm affect your workout, your workout affects your circadian rhythm! If you want to sleep and wake earlier, workout earlier in the day 
• To maximise the effect of exercise on your circadian rhythm, do it outdoors

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Written By Bea: Female fitness expert at MotivatePT – Reps Level 3 Qualified / Pre & Post Natal