“Better sleep comes with regular exercise” is the assertion in numerous studies. However, we sleep specialists usually add the proviso “but not close to bedtime.” We have thought that by raising core body temperature and activating the sympathetic (fight or flight) systems, that exercise right before bed was counterproductive.
Wouldn’t you know, just when we thought we had this all figured out, here comes one of those annoying studies that makes us rethink what we thought was a certainty. In this month’s journal Sleep Medicine, a study based on the 2013 National Sleep Foundation Sleep in America Poll demonstrates how little we may actually know.
In this study, 1,000 people were surveyed regarding time of exercise and quality and length of sleep. The results were rather surprising. As expected, early morning exercisers had the best sleep outcomes. They had the highest likelihood of reporting good sleep quality and lowest likelihood of waking unrefreshed. However, the evening moderate or vigorous exercisers did not differ from non-exercisers concerning their sleep. In fact, the vast majority felt that late exercise either had no effect on their sleep or improved it.
The findings are rather stunning and show that we may have been wrong about the effects of exercise on sleep all along. As the authors point out, it is true that elevated core temperature can hinder sleep, but the rapid drop in temperature occurring soon after exercise may trump that and in fact, help to induce sleep. We also know that after exercise, self-reported anxiety, as well as drops in blood pressure and muscle tension are most evident in the first one to two hours following exercise.
What is the take home message? I, for one, will start to look at timing of exercise differently in my patients with sleep problems. There are many of us who just cannot exercise in the morning, either because of timing or inherent circadian rhythms. It would appear that exercise, even if close to bedtime, is preferable to no exercise. Based upon this study I think all of us need to reexamine our rules of sleep hygiene. Looks like I’m going to have to put a line through number 10 on my sleep hygiene handout, “No exercise within three hours of bedtime.”