This works about ninety percent of the time. The other ten percent of the time, I feel like I have been cheated. Falling asleep is never a problem; it's the waking up at 2:00AM and not being able to fall back asleep that I take issue with.
Dr. Youngstedt from the University of California, San Diego, points out there is little scientific evidence that exercise effects sleep levels in good sleepers; however, in people that suffer from insomnia, there is evidence to suggest moderate aerobic activity might help people with insomnia. Another recent study at the Federal University of Sao Paulo at Brazil suggests moderate aerobic exercise, as opposed to heavy aerobic exercise and strength training, increases total sleep time as well as reduces anxiety.
The Mayo Clinic is quick to point out that any form of exercise helps with stress reduction, including tai chi and walking, primarily because exercise releases endorphins and, as Reese Witherspoon points out in Legally Blond, "endorphins make you happy. Happy people don't kill their husbands." I have often wondered what would happen if all of the world leaders who are currently fighting other countries took up a jogging program. It might be the solution to world peace.
The point is, exercise has many psychological benefits as well as physical. In fact, the psychological benefits may very well outweigh the physical at the end of the day. And hopefully, it leads to a good night's sleep.