A “typical” circadian rhythm is probably an oxymoron; we all run a little differently. Still, each of us operates off a master clock. The precise times vary depending on when you wake up and go to sleep, but certain events happen in predictable intervals. For a rough idea of what that clock looks like, James Clear, on his aptly named James Clear Blog, suggests we imagine an adult who wakes up at 6 am and goes to bed around 10 pm.
At 6 am, light streams through your window, prompting your brain to release a shot of the hormone cortisol to wake you up. Not fully online yet, you might supplement that cortisol with a little friendly caffeine, in the form of a steaming cup of joe.
By seven, adenosine, the hormone designed to sedate you for nighttime rest, is no longer present in your bloodstream. The message is clear: there’s a brand new day waiting for you.
Around nine, your sex hormone peaks. (Of course, what you do with that information is up to you.)
By ten, you are at your daily high point in terms of mental alertness. If there is some critical thinking challenge ahead of you—an important deal to cut, a spreadsheet to build, a whitepaper to write, a speech to make—carpe diem.
At noon, you take in lunch, and your digestive system gets busy converting that food into useable fuel in the form of glucose. This affects your metabolic rate and your blood sugar levels. Just how it affects you somewhat depends on the contents of your plate. If you’ve eaten a lot of carbs, by 1:30 pm, you may be feeling a little tired and cranky.
After your digestive track gets a chance to work its magic, you manage to push through that post-lunch dead zone, and by 2:30 pm, you’re starting in on your second wind. This coincides with the peak of your motor coordination. If you’re thinking about any intricate physical movement, from practicing the accordion to hitting the ballroom to polish your pasodoble, the moment has arrived.
When 3:30 pm hits, you also hit your stride as far as reaction times go. Taking a little batting practice? Trying to get to the next level of Legend of Zelda? It won’t get much better than this.
By 5 pm, your cardiovascular system and muscle strength are at their zenith. Now’s the time to go for that bench press record, or challenge your officemates to a race around the parking lot.
When 7 pm rolls around, your blood pressure and body temperature are at their highest, much like a car engine that’s spent the better part of the day burning up miles on a cross-country road trip. Your brain, however, is not feeling as hot: fatigue has set in, and the quality of your decision-making has eroded by 70% compared to that 10 am sweet spot.
At 9 pm, your body starts preparing for sleep. Your digestive system slows and your bowels begin to suppress, making sleep more comfortable—and, given the alternative, more hygienic.
When darkness falls, your brain revs up its adenosine production, so that by 10 pm, there is enough in your bloodstream to subdue physical movement and conscious thinking, thereby ushering you into a night of peaceful sleep.
2 am finds you in the deepest part of your sleep cycle. If you wake up during this time, the result is grogginess, confusion—and a huge toll on your brain’s memory consolidation process.
When 4 am arrives, your body has fully powered down. You experience mini hibernation. You’ve cooled down to the point where you might find yourself pulling up the covers to squeeze out those last few hours of sleep.
Two hours later, sunlight streams through your window and a new shot of cortisol wakes you up. Another 24-hour circadian revolution draws to a close, a new one begins, and the cycle continues.