New research from Northwestern University (NU) suggests exercise, a popular cure for insomnia, does not necessarily work as expected.

According to a news release from the NU Feinberg School of Medicine, 45 minutes of cardio is not the best way to help someone sleep at night. Previous studies on exercise and sleep have been conducted with healthy sleepers.

"If you have insomnia you won't exercise yourself into sleep right away," said lead study author Kelly Glazer Baron, a clinical psychologist and director of the behavioral sleep program at NU Feinberg School of Medicine. "It's a long-term relationship. You have to keep at it and not get discouraged."

The study, published Thursday in the Journal of Clinical Sleep Medicine, represents the first in-depth look into exercise's lack of help to insomniacs. It also showed people are less likely to exercise after a night of poor sleep.

"Sleeping poorly doesn't change your aerobic capacity, but it changes people's perception of their exertion," Baron said. "They feel more exhausted."

Baron decided to launch the study after her patients with insomnia complained they were not sleeping well despite the recommendations she made to exercise.

"They'd say, 'I exercised so hard yesterday and didn't sleep at all,'" Baron said. "The prevailing thought is that exercise improves sleep, but I thought it probably wasn't that simple for people with insomnia."

Senior author Phyllis Zee, M.D., the Benjamin and Virginia T. Boshes Professor of Neurology at Feinberg and director of the Sleep Disorders Center at Northwestern Memorial Hospital, said exercise needs time to affect sleep.

"Patients with insomnia have a heightened level of brain activity and it takes time to re-establish a more normal level that can facilitate sleep," Zee said. "Rather than medications, which can induce sleep quickly, exercise may be a healthier way to improve sleep because it could address the underlying problem."

Participants in the study were older women with higher presence of insomnia. Baron said older people with issues sleeping should use exercise because drugs can cause damage in advanced age.

"People have to realize that even if they don't want to exercise, that's the time they need to dig in their heels and get themselves out there," Baron said. "Write a note on your mirror that says 'Just Do It!' It will help in the long run."