Sleep: The Chemical Force and Circadian Force

By Mike Hazle, Sep 15, 2021

Part 1 in the series: Re-Engineering Human Performance Through Sleep

The Chemical Force: Adenosine

  • Adenosine builds up the longer we are awake. When you wake up, adenosine levels are low, then begin to slowly rise until they reach very high levels at the end of the day. Higher adenosine levels drive sleep hunger.
  • Caffeine blocks adenosine (antagonist) as it binds to the adenosine receptor and will not allow adenosine to park there. When caffeine wears off, adenosine rushes in and almost doubles in its binding power causing “the crash”.
  • Caffeine increases dopamine, the "feel good and motivated" neurotransmitter. As dopamine goes up, epinephrine goes up as well, and the end result is energy.
Adenosine - The Chemical Force of Sleep

The Circadian Force: The Internal 24-hour Clock

  • If you “pull an all-nighter” you may feel sleepy as the night goes on, but if you stay up longer, you will feel alert again. This is due to the circadian force or circadian rhythm.
  • When adenosine is low because we have slept, a hormone called cortisol is released from your kidneys and a little pulse of epinephrine as well. Think of cortisol as nature's built-in alarm system. This can be stimulated from an alarm or natural waking but it’s important that cortisol release happens earlier in the day.
  • A natural timer is set in your body and your nervous system, so that melatonin gets secreted from the pineal gland about 12-14 hours after the initial cortisol release.
The Circadian Force - Internal 24-hour Clock
  • The Pineal gland is the organ that produces melatonin. That’s the only place it can come from. Melatonin will help you fall asleep but not stay asleep in most cases.
  • Cortisol and melatonin are endogenous, meaning it happens automatically, even if we were in a cave in total darkness.
Sunlight's effect on sleep
  • Sunlight is a huge, influential element that affects your nervous system and sleep process. Exposure to sunlight at dawn and dusk is key to setting your internal rhythm.
  • When sun light comes into the eye (into the Retinal ganglion cells, which are brain neurons in the eye) those cells receive the signal from the light and then distribute that signal to every cell of your body.
  • These cells respond best to sunlight and most sensitive to low solar angle light (yellow and blue contrast that is only available at early sunlight and sunset).
  • Light is 50x less effective when viewed through sunglasses or a window, yet 10-50k lux is sufficient to set the circadian clock.

  • Your circadian rhythms are set on averages based on when you are seeing the brightest blue lights.
  • By viewing sunlight in the evening (sunset), the melanopsin cells signal to the brain that it’s the end of the day. This can help to increase melatonin and protect the body’s mechanisms against negative effects of light exposure later in the day.
  • Phase advance and phase delays: Light exposure in the middle of the night will make it harder for you to wake up in the morning and harder to go to bed later, and vice versa. It is important to give your neurons and internal mechanisms an anchor to hold onto for timing and rhythm as these systems run on averages.
  • Naps can be beneficial if they are less than 1 ultradian sleep cycle and you don’t go into REM sleep, with 20-40 minutes being the sweet spot.

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About the author

Mike Hazle

Human Performance & Education Specialist

Articles by Mike Hazle >

After a 10-year career on the World Athletics Tour and the Olympics, competing in 23 countries, winning 5 National Championships medals, working with the world's elite Special Operators as a U.S. Air Force Special Warfare Combat Controller (CCT)...Mike was left injured, exhausted, and empty inside even after achieving what most would call "The American Dream." A dream full of glamour, lights, material wealth and superficial possessions.

Over the years, the lights and fireworks of the Olympic stadium have faded and the wounds of Special Operations Training have healed. Mike has learned lessons from a life in the arena of the world's most stressful environments. These lessons will carry him farther than any athletic accomplishment or experience he has ever had. Now, his unwavering mission is to help people across the world learn the tools and techniques he has mastered and help them recover from high impact, high stress careers.

In his expansive 20-year career, on top of the highest level of athletics on the World's largest stages and Military Special Operations, Mike has been educated from the best sports physiologists, nutritionists and strength & conditioning coaches across the globe. Not only that, Mike has picked up along the way a master’s degree in Sports Management, a Bachelors in Kinesiology, a National Strength and Conditioning Association (NSCA) Certified Strength & Conditioning Specialist (CSCS) and Cross Fit certifications. Mike has also spent 6 years on the resident athlete advisory board at the US Olympic Committee's (USOC) Olympic Training Center in Chula Vista, CA.