A new study suggests that poor sleep quality predicts lower physical activity in people with post-traumatic stress disorder (PTSD).

“We found that sleep quality was more strongly associated with physical activity one year later than was having a diagnosis of PTSD,” said lead author Lisa Talbot, postdoctoral fellow at the San Francisco VA Medical Center and the University of California, San Francisco. “The longitudinal aspect of this study suggests that sleep may influence physical activity.”

In other words, people are more likely to exercise is they get a good night’ sleep.

The study involved data from the Mind Your Heart Study, a prospective cohort study of 736 outpatients recruited from two Department of Veterans Affairs (VA) medical centers.

PTSD was assessed using the Clinician-Administered PTSD Scale (CAPS).

Participants rated their sleep quality overall during the last month, at baseline and again one year later. They reported the level of physical activity during the last month. Of the 736 military veteran participants, 258 had current or subsyndromal PTSD.

According to Talbot, the results suggest that behavioral interventions to increase physical activity should include an assessment for sleep disturbance.

According to the National Center for PTSD of the U.S. Department of Veterans Affairs, PTSD symptoms such as nightmares or flashbacks usually start soon after a traumatic event, but they may not appear until months or years later.

Symptoms that last longer than four weeks, cause great distress, or interfere with daily life may be a sign of PTSD.