What does exercising right before bed do to my sleep?

Exercise improves sleep, even when you do it at a random point in the day. A single workout already produces small positive effects: you fall asleep a little faster, sleep a little longer and more efficiently, and get slightly more deep sleep. People who move regularly over several weeks see the biggest improvements in the time it takes to fall asleep and in overall sleep quality.

The feared effect of evening exercise on sleep turns out to be less of a problem in practice. Twelve weeks of moderate aerobic training showed that exercising up to 8 p.m. shortens the time it takes to fall asleep, just as morning exercise does. Your body clock does not shift earlier the way it does with morning exercise, but your sleep does not suffer either. Evening exercise even had an extra benefit in that study: blood vessels responded better and blood pressure dropped more than with morning exercise. Training very late and very intensely is a different matter; there is too little data there to draw firm conclusions.

If you are specifically dealing with sleep problems, some forms of exercise have the strongest evidence behind them. Yoga produces the biggest gain in total sleep time for people with insomnia, on average almost two hours more. Walking or jogging reduces the severity of insomnia most on a standardised symptom scale. For older adults, strength training appears to improve sleep quality the most of all individual forms of exercise. A combination of endurance-strength training with walking scores even better in older people than either approach on its own.

How exercise influences sleep is not yet fully understood. There are signs that physical activity lowers the stress hormone cortisol, and that this partly explains why sleep improves. That link has not been firmly proven, however, and the studies that looked into it involved mainly women who had been treated for breast cancer, which makes it hard to apply the findings more broadly.