Evidence for sleep impairment is conflicting, however. Youngstedt et al (1999) examined the influence of prolonged, vigorous late-night exercise on sleep in 16 highly fit male cyclists. Each completed two 60-hour laboratory treatments involving a baseline night, an experimental treatment night, and a recovery night. Each subject completed two tests: cycling for three hours at 65-75% of heart rate reserve combined with bright light exposure and exposure to a three-hour pulse of bright light alone. The order of testing was randomised. On the treatment night, exercise and bright light or the bright light alone was centred at six hours before their usual waking times, followed by bedtimes 30 minutes after the treatments. Sleep was assessed with an Actillume wrist monitor for sleep onset, wakefulness after sleep onset and total sleep time, besides subjective assessments of sleep quality.
The main finding of the study was that exposure to bright light or the addition of exercise to a three-hour exposure to bright light, ending 30 minutes before bedtime, did not alter sleep patterns. In conclusion, vigorous exercise before bedtime does not have an adverse effect on sleep.
Source: SD Youngstedt, DF Kripke, JA Elliott Medicine and Science in Sport and Exercise, 31, 6:864-869, 1999.