Working out is great for your body and mind – and it can also help you get a good night’s sleep. But, for some people, exercising too late in the day can interfere with how well they rest at night.

Based on available studies, “We have solid evidence that exercise does, in fact, help you fall asleep more quickly and improves sleep quality,” says Charlene Gamaldo, M.D. , medical director of Johns Hopkins Center for Sleep at Howard County General Hospital. “But there’s still some debate as to what time of day you should exercise. I encourage people to listen to their bodies to see how well they sleep in response to when they work out,” she adds.

How Exercise May Help You Sleep

Researchers don’t completely understand how physical activity improves sleep. “We may never be able to pinpoint the mechanism that explains how the two are related,” she says. 

However, we do know that moderate aerobic exercise increases the amount of slow wave sleep you get. Slow wave sleep refers to deep sleep, where the brain and body have a chance to rejuvenate. Exercise can also help to stabilize your mood and decompress the mind, “a cognitive process that is important for naturally transitioning to sleep,” says Gamaldo.

The Timing of Exercise May Matter

Some people may find that exercising close to bedtime seems to keep them up at night, says Gamaldo. How does working out affect the mind?

• Aerobic exercise causes the body to release endorphins. These chemicals can create a level of activity in the brain that keeps some people awake. These individuals should exercise at least 1 to 2 hours before going to bed, giving endorphin levels time to wash out and “the brain time to wind down,” she says.
• Exercise also raises your core body temperature. “The effect of exercise in some people is like taking a hot shower that wakes you up in the morning,” says Gamaldo. Elevation in core body temperature signals the body clock that it’s time to be awake. After about 30 to 90 minutes, the core body temperature starts to fall. The decline helps to facilitate sleepiness.

Despite these biological responses to exercise, other people find that the time of day they exercise doesn’t make a difference. “Whether it’s in the early morning or close to bedtime, they’ll see a benefit to their sleep,” says Gamaldo. 

“Know your body and know yourself,” she says. “Doctors definitely want you to exercise, but when you do it is not scripted.”

How Much Exercise You Need for Better Sleep

Patients often ask Gamaldo how much exercise they need for better sleep, and how many weeks, months or years it will take to experience this benefit. 

The good news: People who engage in at least 30 minutes of moderate aerobic exercise may see a difference in sleep quality that same night. “It’s generally not going to take months or years to see a benefit,” says Gamaldo. “And patients don’t need to feel like they have to train for the Boston Marathon to become a better sleeper.” 

Moreover, while many studies focus on aerobic activity and sleep, Gamaldo says picking an exercise you like will help you stick with it. For example, power lifting or an active yoga class can elevate your heart rate, helping to create the biological processes in the brain and body that contribute to better quality sleep, she says. 

“We really want to encourage people to exercise, just be mindful of timing and whether it seems to affect your ability to get optimal sleep quality,” she says.