To maintain a healthy lifestyle, understanding our natural circadian rhythms can have a huge impact on how we plan our sleep schedule, work, and workout times for optimal functioning and peak performance.Circadian rhythms are biological rhythms that align to the 24-hour day and peak at different periods of the day and night related to different biological processes. This rhythm initiates various biological processes within our bodies to keep us functioning at our best when we need to and to rest and recover when we need to.
The brain contains a central pacemaker (like an internal clock) in the suprachiasmatic nucleus in the hypothalamus. This location allows our biological clock to keep our systems running no matter what’s happening externally.
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A Break Down of the Circadian Cycle
Here’s a look at the average circadian cycle:
3am to 7am: Lowest energy
6:45am: Sharpest blood pressure rise as you prepare to wake up
7:30am: Melatonin secretion stops
8:30am: Bowel movements
10am-1pm: Highest alertness and energy
1-3pm: Afternoon slump
2:30pm: Best coordination
3:30pm: Fastest reaction time
5pm: Best muscular strength/cardiovascular efficiency
9pm: Melatonin secretion starts
10:30pm: Bowel movements suppressed
Working with the natural rhythms of your body can help you avoid feeling like you’re fighting against yourself all the time. Start to pay attention to how you feel during the day. Does it match up with the average cycle?
Pay attention to when you feel the most alert and energetic and see if you can squeeze a workout in during that time window. The closer you can shift your daily schedule to match these rhythms, the easier it will be to maintain your routines (and reach your health and fitness goals!).
Which Processes does the Circadian Rhythm Affect?
Sleep-wake cycle: The circadian rhythm drives alertness and sleepiness through hormone secretion.
Blood pressure: BP levels change during the sleep/wake cycle and have their sharpest rise at 6:45am as the body prepares for wake-up.
Body temperature: Body temperature is at its lowest at 4:30am to facilitate REM sleep and at its highest at 7pm.
Bowel movements: No one wants to be woken up in the middle of the night for a bowel movement! Thankfully, the body slows that process starting at 10:30pm.
Hormone secretion: The body starts secreting melatonin when it’s time for bed and stops secreting it when it’s time to wake up. Testosterone is also secreted at its highest at 9am, helping you feel alert and awake.
What Happens If Your Circadian Rhythm is Out of Whack?
With so many body processes impacted by the circadian rhythm, it’s not hard to imagine that a rhythm gone rogue would wreak havoc on your overall health, not to mention productivity during the day. Circadian misalignment occurs when your internal circadian rhythm is no longer aligned with the biological night.
Your first indicator will be that your sleep/wake cycle seems “off”. You might notice that you aren’t able to fall asleep at bedtime or wake up when it’s an appropriate time to get up. If this only happens occasionally, you probably don’t need to worry too much. If you notice that your sleep pattern is regularly disrupted, it might be worth looking into to find the root cause of the issue. Circadian misalignment can lead to cardiovascular disease, obesity, diabetes, cancer, or psychiatric and mood disorders.
A Note on Shift Work
Someone who does shift work is at an increased risk of developing circadian misalignment because their sleep/wake schedule may not occur during regular hours. If you happen to work a night shift, there are steps that you can take to keep your circadian rhythm as healthy as possible!
• You’ll want to ensure that your work “day” mimics the actual day as much as possible by trying to get light exposure, eating regular meals, and avoiding too much caffeine within 6 hours of bedtime.
• Plan exercise just like you would if you worked regular hours. If your energy is low, or you’re working out after your shift, choose low-intensity exercise and just do what you can. I’ve had clients come in for a workout before their night shift to start their day just like a client working a 9-5 job would do, and that seemed to work well for them.
• Also, try to make sure your “night” mimics the actual night as much as possible by darkening your room and sleeping without distraction.
Tips to Improve Circadian Rhythms & Sleep
• Try to get exposure to natural sunlight. Especially early in the day, to help align your circadian rhythm with the biological day. If you are a shift worker, you might try using a sun lamp.
• Follow a consistent sleep schedule. As tempting as it is to sleep in on the weekends, this can leave you feeling more tired during the week as your body tries to figure out what “time zone” it’s living in.
• Exercise daily to make it easier to fall asleep at night, not to mention, to reach those fitness #goals.
• Avoid caffeine after noon, especially if you’re having trouble sleeping. Not everyone is equally sensitive to caffeine, so this might take a bit of experimenting on your part to find what caffeine routine works best for you.
• Limit light before bed. This means shutting down electronic devices an hour before bedtime to avoid exposure to blue light, which can confuse your circadian rhythm into thinking that it’s “wake up time”.
What Hormones Are Affected by Circadian Rhythms?
• Melatonin, growth hormone, cortisol, leptin, and ghrelin are all highly regulated by the circadian rhythm.
• Melatonin is a hormone produced and released at night (or in response to dim light) to promote restorative sleep.
• Growth hormone regulates the fat, muscle, tissue, and bone in our bodies and other aspects of metabolism.
• Cortisol is the primary stress hormone. In addition to helping you in a fight-or-flight situation, it also impacts glucose release in the bloodstream, your brain’s ability to use glucose, and enhances tissue repair.
• Ghrelin promotes hunger and leptin suppresses hunger, making their healthy function vital to maintaining a healthy weight.
A healthy functioning circadian rhythm can keep these hormones in check to promote overall health and well-being. In terms of your health and fitness goals, having proper hormone balance is vital to your overall performance, recovery, and results.
Bottom line: While your circadian rhythm does ensure that you get adequate rest, it also regulates physiological function during the day so that you can think, move, and function well. The more closely you can align your schedule with your body clock, the better off you will be!
Kim, T. W., Jeong, J. H., & Hong, S. C. (2015). The Impact of Sleep and Circadian Disturbance on Hormones and Metabolism. International Journal of Endocrinology, 2015, 1–9. https://doi.org/10.1155/2015/591729
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National Institute of General Medical Sciences. (2022). Circadian rhythms. National Institutes of Health. Retrieved May 11, 2022, from https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx#:%7E:text=Circadian%20rhythms%20are%20physical%2C%20mental,the%20study%20of%20circadian%20rhythms.