THE Black Dog Institute is challenging Australians to do at least one hour of physical activity a week to improve their physical and mental health as part of Exercise Your Mood week to May 6.

The campaign follows a recent study, led by the Black Dog Institute, that found even a small amount of physical activity - as little as one hour each week - may protect against depression, regardless of age, gender or fitness level.

Black Dog Institute associate professor Sam Harvey said the exercise habits of many Australians were concerning.

"In Australia we still have many people suffering from depression, but there is a lot of exciting research that is beginning to tell us how we may be able to reduce the amount of depression in our communities,” she said.

"Our study shows that encouraging people to take just a small amount of exercise each week could have a significant impact on depression rates more broadly.”

Black Dog Institute ambassador Michelle Bridges said she had seen first-hand the positive impact exercise could have on a person's mental health, which was why she was so passionate about getting people moving.

"We're not talking running marathons or climbing Everest here. Just adding in a little bit of extra activity can really make a big difference,” she said.

According to the Australian Health Survey, 20 per cent of Australian adults do not undertake any regular physical activity, and more than a third spend less than 1.5 hours per week being physically active.