Exercise can release feel-good chemicals in the brain
People with depression are still being denied exercise on prescription, a report suggests.
In 2004, clinical guidelines recommended exercise as a treatment for mild or moderate depression.
But the Mental Health Foundation study found only half of the country's GPs have access to exercise referral schemes for people with depression.
One in six people experience depression, with the recession expected to fuel rates.
Recent figures show that prescriptions for antidepressants have almost doubled in a decade, from 18,424,473 in 1998 to 35,960,500 last year.
But evidence shows that a supervised programme of exercise on prescription can be as effective as antidepressants in treating mild or moderate depression - and unlike drugs carries no risk of side effects.
The latest report suggests lack of funding is limiting patient access to exercise referral schemes.
However, it also finds that many GPs are not aware that exercise schemes are available in their area.
The Mental Health Foundation is calling for primary care trusts to invest in developing new schemes.
Andrew McCulloch, Chief Executive of the Mental Health Foundation, said: "This is not about knocking antidepressants, they can be incredibly helpful for some people but the truth is that their side-effects can be unpleasant.
"People experiencing mild or moderate depression are currently being denied access to a clinically recommended, medication-free treatment that could help them.
"Primary Care Trusts really need to make an effort to ensure that exercise therapy is available to GPs and their patients."
Central YMCA, a charity promoting the benefits of physical activity on mental health, runs exercise referral programmes.
Rosi Prescott, its chief executive, said: "Despite the increasing evidence base to support exercise therapy, much more needs to be done to persuade those in the health service of their benefits."
Dr Mike Dixon, chairman of the NHS Alliance, which represents primary care groups, said doctors should do more to make exercise schemes available to their patients.
He said such schemes were not expensive to run, but some clinicians had been slow to embrace the concept.
He said: "There is certainly a role for such a straightforward, simple treatment for depression.
"It is a great pity that doctors tend to press the biomedical button, rather than one which enables patients to help themselves.
"Unfortunately, we are taught so much as medical school to look for a biomedical solution involving drugs or procedures, rather than to consider self-help options."
The National Institute for Clinical Excellence recommends that patients with mild or moderate depression should follow a structured and supervised exercise programme of up to three sessions of exercise, each lasting 45-60 minutes, a week.