Sleepless and sedentary? Instead of counting sheep in a field, try running through a meadow.

Experts agree that an aerobic exercise routine during the day can keep you from tossing and turning at night, even if they're not sure why.

The bottom line is we really don't know why people tell us that exercise helps them sleep, said Dr. David Davila of the National Sleep Foundation.

But if people are normally active, reaching their aerobic goals, chances are they will sleep the right amount for what they need.

Davila, who practices sleep medicine in Little Rock, Arkansas, said the low-grade sleep deprivation suffered by many time-pressed, under-rested Americans has a cumulative effect.

People have more car accidents and what they call 'presentee-ism', or poor performance, at work, he said. There are fallouts for the average person.

But evidence is emerging that aerobic exercise can offer relief from insomnia.

A recent study at Northwestern University in Chicago, Illinois tracked 23 previously sedentary adults, primarily women 55 and older, who had difficulty falling or staying asleep.

After 16 weeks on an aerobics training program that included exercising on a treadmill or stationery bicycle, average sleep quality improved.

Most of poor sleepers became good sleepers, said Dr. Phyllis Zee, the lead researcher in the study, which was funded by the National Institute on Aging.

She said an earlier study using Tai Chi showed less dramatic results, as did a control group doing non-physical activities such as cooking classes and museum lectures.

This is the first time that I'm aware of where we've looked at the benefits of aerobic exercise as a treatment modality in a population with insomnia, Zee said.

She added that she sees a lot of patients with insomnia, which afflicts 25 percent of the population and can reach as high as 40 percent in older people.

We tell them to get regular exercise. But we really don't emphasize how to exercise.

If your schedule dictates that you can only hit the gym at 5 a.m. Dr. Shawn D. Youngstedt, an expert on sleep and exercise at the University of South Carolina, believes that an hour of exercise can do more good than an extra hour of sleep.

There's no scientific evidence that people need eight hours, seven is fine, he said. It's far clearer that exercise has wonderful benefits. It's better than drugs for diabetes, mental health, cancer prevention.

Dr. William Roberts, of the American College of Sports Medicine, cautions that for some people the time to exercise is not an hour before bed.

To exercise close to sleep time is not good for everyone, he explained. Try to get a half hour to an half hour of exercise early enough in the day and try to sleep on same schedule.

Roberts suggests doing something calming to wind down.

Do not play video games, he said. Read away from bed and then go to bed. Avoid caffeine and other stimulants before turning in.

The improved sleepers in Zee's study also reported better moods, fewer depressive symptoms and enhanced vitality.

Vitality is everything, Zee said. It's how somebody feels, how alert. If you think about the complaints of poor health, people will always say, 'I feel so tired.'