Answered by Janet Lee on Monday, June 1, 2009
That depends on why you're going to bed late in the first place, says Sonia Ancoli-Israel, Ph.D., director of the Sleep Disorders Clinic at the San Diego Veterans Hospital and author of the book All I Want is a Good Night's Sleep. "There's a certain circadian rhythm [the internal clock, of sorts, that dictates your sleep-wake cycle] called Delayed Sleep Phase, in which people can't fall asleep before one or two in the morning," says Ancoli-Israel. "It's most common in teenagers and adolescents, who eventually outgrow it, but some people don't shift back." If you fall into this category, exercise won't make a difference. If, however, you're staying up late because you just can't fall asleep, exercise might be a good way to adjust your rhythm.
Studies have shown that people who are physically fit sleep better in general, but exercising right before bed can actually sabotage your sleep cycle. "Our sleep-wake propensity is controlled by body temperature," says Ancoli-Israel. "Exercise raises your body temperature." Consequently, if you exercise right before bed, your body's feeling very awake. She suggests planning a workout about six hours before your desired bedtime to give your body a chance to cool down. As your temperature dips, you'll get sleepy.