And since exercise releases endorphins and brings more oxygen to the brain, doing so close to bedtime—but not too close—may help get you in the right mindset for sleep. One 2018 review in the journal Sports Medicine found that evening exercise did indeed help people fall asleep faster and spend more time in deep sleep stages, seeing as it wrapped up at least an hour before bedtime. Exercising at night may also be more physically rewarding, as research has found that it takes about 20% longer to reach exhaustion in the evenings compared to the mornings.
It's worth pointing out that someone's sleep habits, types of workouts, and age can all affect this ideal exercise window. For example, Harris, a distance runner, says that she used to have no problem running close to bedtime but stopped being able to train at night once she reached her mid-30s.
These days, she exercises in the morning—which she's found neither helps nor hurts sleep quality. However, she cautions that people who have trouble sleeping through the night and tend to wake up super early should avoid morning workouts, as they can train your body to keep waking up at that time.