The effects of the fight-and-flight response (technically, the sympathetic nervous system) on sleep explain how and why exercise has such important, well-known effects on sleep. If you run a mile at top speed or lift heavy weights just before going to bed, you’ll probably have a hard time falling asleep because vigorous physical activity turns on this system, stimulating arousal. In contrast, a good dose of physical activity earlier in the day like a game of soccer, an hour or two of gardening, or a long walk helps sleep come more easily.
