Sleep

[lt.wolf]

How Exercise Helps (and Hurts) Sleep
A single workout won't fix your sleep problems, but a consistent habit might.
By Alex Hutchinson
Published August 21, 2013
2012_Nov_EliteSleep
Exercise helps you sleep better, right? That's the conventional wisdom, and has certainly been my experience. But for others, the opposite seems to be true. An interesting new study in the Journal of Clinical Sleep Medicine offers an explanation for this apparent paradox, as Gretchen Reynolds reported in the New York Times today.

Actually, it's a reanalysis of the data from an earlier study by researchers at Northwestern. That initial study produced the expected result: a group of sedentary older adults with persistent insomnia did three days a week of aerobic exercise for 16 weeks, and by the end they reported better sleep quality and were getting an extra 45 minutes of sleep per night compared to the control group. Wonderful.

But a closer look at the data reveals some surprises. For one thing, there was no link between the amount of the exercise the subjects did on any given day and how they slept that night. So it wasn't as simple as exercising to make yourself tired and then sleeping more as a result. Also, sleep quality and duration hadn't improved at all after eight weeks -- it was only by the end of the study that the improvement was clear. Eight weeks is still a long time, so it's easy to imagine that some people who try exercise as a sleep aid give up after seeing little improvement.

So why the long delay before effects were observed? The researchers suggest that people with insomnia are essentially wired a bit differently -- their stress response is abnormally sensitive. A single bout of exercise might even ramp up that stress response even more, but over time regular exercise helps to dial it back. The take-home message: for sleep, as with most of exercise's benefits, it's the consistent habit that makes the biggest difference, not any one super-workout.

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