Can exercise timing shift circadian rhythms?

Question

Particularly for shift workers, can exercise timing delay circadian rhythms so that going into a night shift, they can feel more alert? What mechanisms are involved in this? Is it to do with melatonin?

Answer 1

Hello Shana!

Our current understanding of Circadian Rhythm is that there are two mechanisms used by our brains to determine our sleep/ wake cycle. The first one is light entrainment. In our eyes, light acting on melanopsin receptors (separate from rods and cones!) stimulates our suprachiasmatic nucleus (SCN) which tells our adrenal gland to secrete cortisol. If there is no light (because its dark at night!) the SCN tells the pineal gland to secrete melatonin. So, melatonin secretion begins at dark and peaks in the night. Cortisol production begins shortly before we wake up, stimulating our arousal from sleep. This is the hormonal controller of sleep/wake.

The second process is a genetic regulation of sleep/wake. The SCN produces two proteins: Clock and Cycle. When these two proteins interact, they form a dimer. This dimer moves into the nucleus of the cell and acts as transcription factors to instigate the expression of per and cry genes. These genes make Per and Cry proteins. Per and Cry combine and this complex acts to negatively inhibit the activity of Clock/ Cycle dimers. The Per/Cry complex degrades with time. Specifically, it takes approximately 24 hours for these proteins to degrade, disinhibiting Clock and Cycle, starting this whole process over.

This finding earned the Nobel Prize in 2017.

So, sort of. Exercise can induce the production of cortisol (countering the melatonin secretion), increase blood oxygen, and reduce the occurrences of alpha waves which begin just prior to sleep. Assuming you are exercising and working in the light, this light also interferes with melatonin production.

If you have ever taken melatonin, you may know that it doesn't immediately put you to sleep. It actually only lasts for about 20 minutes in our blood before being broken down. Countering this melatonin-induced sleepiness is manageable with light, exercises, and stimulant drugs (caffeine). However, there are well documented side effects to switching to a fully nocturnal schedule. While you can keep your brain awake during the night, our circadian rhythm also controls other bodily actions such as metabolism. This can affect how we store energy from food and how we process/ metabolize what we ingest (such as food, drinks, and drugs).

Either way, establishing a routine for your body and mind will absolutely help keep yourself regular. And exercising at night can help you stay awake later, give you a little boost of the good stress and that good oxygen. Good questions, I hope this helps!

Answer 2

Yes, exercise timing can shift circadian rhythms, and it can be beneficial for shift workers to optimize their alertness and performance during night shifts. Exercise can shift the timing of the circadian rhythm by affecting various physiological processes, including the release of hormones such as cortisol and melatonin, and the regulation of body temperature.

Research has shown that regular exercise can help to synchronize the circadian clock with the external environment, which can lead to improvements in sleep quality, mood, and cognitive performance. Exercise in the morning has been found to advance the timing of the circadian rhythm, while exercise in the evening can delay it.

For shift workers, exercise timing can be used strategically to adjust their circadian rhythm to match their work schedule. For example, exercising in the morning before a night shift can help to delay the circadian rhythm and promote alertness during the shift. On the other hand, exercising in the evening after a night shift can help to advance the circadian rhythm and promote better sleep during the day.

The mechanism behind the circadian rhythm shift caused by exercise is not fully understood, but it is thought to be related to the interaction between the circadian clock and various physiological systems, including the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Melatonin, which is a hormone that regulates the sleep-wake cycle, may also play a role in the circadian rhythm shift caused by exercise.

Overall, exercise timing can be a useful tool for shift workers to optimize their circadian rhythms and promote alertness and performance during night shifts.