A reader—OK, my friend Beth—wrote me with a question: Is exercising at night likely to make it more difficult to fall asleep afterwards?
I haven't had trouble falling asleep since the summer I saw Poltergeist, so I called Shawn Youngstedt, a researcher in the department of exercise science at the Arnold School of Public Health at the University of South Carolina, who has studied the question. He says it's a common assumption that working out too close to bedtime impairs sleep, but that the evidence suggests otherwise.
In general, he says, exercise at any time of the day actually helps people without sleep disorders sleep a bit better, and the effects on people with insomnia or disturbed sleep appear to be even greater. No one knows exactly why; it could be that exercise reduces the anxiety that can make sleep difficult or that it cuts down on physiological arousal. Both surveys and experimental evidence suggest that sleep is improved or at least not disrupted even if it's performed up to a half-hour before bedtime, says Youngstedt. That's important, because "for a lot of people, exercising in the evening is the most convenient time," he says.
However, it is possible that some folks are exceptions and need to "practice" to be able to fall asleep quickly after working out. And because most of the studies have been done using steady aerobic exercise, it's possible that something that gets your brain working a bit more, like tennis or basketball, might have different effects. So experiment with your own routine. But don't let the fear of sleep problems stop you from working out.