They found that for most people, nocturnal exercise did not interfere with their overall nighttime sleep – with one caveat. “If the exercise ended less than two hours before bedtime, sleep was negatively affected,” Frimpong said in a press release. “Participants took longer to fall asleep and the length of sleep decreased.”
Exercises completed two to four hours before bedtime did not interfere with sleep in the same way. Indeed, Frimpong stated, “Our analysis showed that there were sleep benefits of stopping exercise two hours before bed, including promoting sleep and sleeping longer.” Interestingly, however, those who exercised two to four hours before bed spent less time in REM sleep – the most dreaming phase – compared to a no-exercise control.
Overall, the study concludes that early evening exercise, two to four hours before bedtime, appears to help, and not harm, sleep – especially for those who spend most of the day sitting down. In the studies examined, cycling was the sport that best supported deep sleep, and night owls tended to benefit more from evening exercise than early risers.