Katy Read / (Minneapolis) Star Tribune

Shannon Hyland-Tassava tries to run up to 25 miles a week, year round. It’s harder in winter — icy sidewalks, snowy trails — but she’s determined. As a sufferer of seasonal mood problems, Hyland-Tassava runs for her emotional as well as physical health.

“Starting a few years ago, I just really started feeling the classic things you always hear about when it came to seasonal mood changes: more tired, more lethargic, more irritable, less motivated to be active and go out and do,” said the 41-year-old from Northfield, Minn. “In the spring and summer, I typically felt fantastic.”

A couple of years ago, on the advice of her nurse practitioner, she started using a broad-spectrum light box and found it helpful. Running is her other important therapy.

“I get such benefit, mentally, from running outdoors,” said Hyland-Tassava, a psychologist and the author of “The Essential Stay-at-Home Mom Manual.” Hyland-Tassava works as a life coach (www.shannontassava.com) and often recommends outdoor activity for her clients. “I firmly believe in the power of exercise to affect mood positively and there’s very strong research to support it.”

Indeed, research suggests exercise can be as effective as medication in combating depression — and comes with positive side effects instead of negative ones, said Beth Lewis, a University of Minnesota psychologist who studies exercise psychology. Even the mildly melancholic can share in this prescription-free mood booster.

How much exercise? No need to train for a marathon: Even 150 minutes a week of moderate-intensity activity (e.g. walking the dog) can provide “significant health benefits,” Lewis said. But studies show only a small percentage of Americans do even that much.

If you haven’t been active for a while, start small, Lewis suggested: “Getting out of the house for 10 minutes is something.” Since SAD and winter blues are linked to loss of sunlight, logic suggests that midday outdoor exercise would be especially beneficial, although indoor exercise helps, too.

Looking ahead to future winters, those who suffer from seasonal mood problems are better off forming an exercise habit long before the symptoms kick in, Lewis said. “Prevention is always better than treatment.”

Once depression has you in its clutches, it has a way of holding you fast to the couch. Dr. Scott Crow, a psychiatry professor at the University of Minnesota who has focused on mood disorders, said, “If you’re stuck enough, exercise is hard.”