Exercise and Sleep

When you are active, the body assumes it's daytime.

This is one reason it's good to get out of bed and do some exercise in the morning before eating—before doing anything else. It gives the body an undeniable signal that the day has started.

Morning exercise also helps people get to sleep at night. In some studies, mice who have the chance to engage in a period of exercise go to sleep earlier and get up earlier than those who don’t exercise. Even a single bout of intense exercise can shift a mouse’s circadian rhythm. Human studies aren’t quite that dramatic, but it’s clear that regular exercisers report less trouble getting to sleep. 

In one study, people went to live in an isolation facility so that they would have no idea what time of day it was. They lived on a slightly shortened day, so that each night they were told to try to get to sleep about twenty minutes earlier than the previous night. Think of it as experiencing jet lag in short, daily intervals. 

Some were told to exercise, and others were not. After about six days, those who were required to exercise were adapting to the changing sleep cycle much faster than those who did no exercise. [2] The change was happening inside their brains with a higher production of melatonin (the brain’s natural sleeping pill). Their brains were releasing melatonin earlier, which made them able to sleep earlier.

Here’s where it gets really interesting, though: these same subjects were then asked to exercise at different times of the day. Those who exercised in the afternoon or at night did not get the same shift in melatonin production. In fact, intense exercise close to bedtime actually delayed the production of melatonin, making it harder for them to go to sleep when the lights went out. [3] It turns out that exercise at the wrong time of day confuses the body’s central regulator of the circadian clock, which in turn confuses the body’s cells and systems.