Doctors often recommend exercise for insomnia but a new study says that it does not cure sleeping disorders.

Researchers from Northwestern University stated in a new study  that though exercise is often prescribed as a treatment for insomnia, running for 45 minutes on a treadmill one day doesn't guarantee a good night's sleep.

"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 Northwestern University, Feinberg School of Medicine. "It's a long-term relationship. You have to keep at it and not get discouraged."

This is the first study that looked into how exercising during the day doesn't guarantee improved sleep that same night and how people tend to exercise less the day following a night of disturbed sleep.

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

Researchers of the study found that exercise and sleeping disorders affect each other in both directions. Researchers found that though long-term exercising results in better sleep, a night of poor sleep can reduce the amount of exercise a person does the following day. Thus, it is safe to say that sleep has the upper hand when it comes to exercising and health problems.

For the study researchers analysed data from a 2010 clinical trial that showed how aerobic exercise improves sleep, mood and vitality over a 16-week period in middle-age-to-older adults with insomnia. The study examined 11 women ages 57 to 70.

"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."