The only thing cuter than watching a puppy run around and exercise is watching a puppy fall fast asleep immediately afterwards. It's adorable, and there are millions of YouTube videos to prove it. While us adult humans are not nearly as cute as puppies on any given day, and most of us don't fall asleep immediately after working out, there's reason to believe that physical activity and exercise can improve our sleep as well.
"In general, the majority of the evidence does support that exercise improves sleep," says Christopher Kline, PhD, assistant professor in the department of health and physical activity at the University of Pittsburgh. In an acute sense, exercise helps you "burn off energy," which makes you fall asleep. But there are a few more scientific ways to explain how this works.
The main belief is that exercise can lead to a buildup of adenosine, a hormone in the part of your brain that monitors your fatigue levels, Dr. Kline says. When you have increased adenosine levels, it helps you sleep, and can actually trigger non-rapid eye movement (REM) sleep or slow wave sleep. Exercise also raises your body temperature, which causes the blood vessels in your extremities dilate to get rid of heat, he says. If you work out in the evening, this change in body temperature helps you drift off to sleep as well.
Beyond the acute effects of exercise, we know that "maintaining a regular, consistent pattern of exercise leads to better sleep on the whole," Dr. Kline says. "It may be due to the mental health benefits." Working out reduces stress, anxiety, and depressive symptoms that may keep you awake at night, he says. In other words, exercise helps you relax so you have an easier time drifting off to sleep at night.
So, now you're likely wondering how to hack your workouts so they make you sleep. In truth, there haven't been enough studies about which specific workouts are the best for improving sleep, so it's tough to say, Dr. Kline says. There's a smattering of research that looks at the differences between the effects of aerobic exercise and resistance exercise, but the results aren't conclusive, he says. And, as you may have predicted, mind-body workouts that focus on relaxation, like yoga and tai chi, seem to be good for sleep as well.
But we can assume that the level of exercise intensity does matter, Dr. Kline says. Moderate to vigorous workouts (like walking at a brisk pace or running if it's not too difficult) tend to be better than lighter intensity workouts (like doing housework), for example, he says. "There's an anecdotal sense that vigorous is a little bit more effective," he says.
Another important factor that seems to be completely up in the air is the best time of day to work out. "What I recommend is really just whenever you can fit it in; I don't think there's a clear-cut optimal time of day," Dr. Kline says. There used to be a common belief that you shouldn't work out before bed, because it will disturb your sleep, but in the past couple years that recommendation has changed, he says. "Some people are much more reactive to late-night exercise, in the sense that it activates them and they're aroused," he says. "But I think for most people, late-night exercise shouldn't be a concern."
Basically, there is not one type of workout that is best for sleep, because we are all different. To that same point, if you're someone who has a sleep disorder like insomnia, then exercise might not be the magic solution. But regardless, it's a good idea to find a workout that you enjoy, so that it can become part of your routine, Dr. Kline says.