Doctors don't prescribe enough exercise to patients despite all the evidence showing its benefits in fighting illness, according to experts, including the chief doctor of the Gold Coast Commonwealth Games.

A doctor's own attitude towards physical activity can also predict their willingness to prescribe exercise for their patients, say a trio of researchers in a scholarly opinion piece in the Medical Journal of Australia.

Just as doctors probe about smoking and drinking, they should be asking patients about how much they exercise in every consultation, according to the comments published on Monday.

Commonwealth Games Chief Medical Officer Dr Anita Green and her colleagues have urged doctors to remember the "considerable evidence" that shows exercise can improve mental health and combat diabetes, the onset of dementia, cardiovascular disease, musculoskeletal conditions and some cancers.

"For some chronic conditions, specific exercise prescription is at least as effective as drug therapy, such as for the prevention of type 2 diabetes and the treatment of depression," Dr Green and her colleagues wrote.

"Yet there remains a large evidence-practice gap between physicians' knowledge of the contribution of physical inactivity to chronic disease."

The researchers said a lack of undergraduate and postgraduate training in physical activity prescription was preventing meaningful change.

"(It) must be addressed in order to increase the knowledge, confidence and skills of physicians in prescribing exercise as medicine to their patients," wrote authors Dr Green, Dr Craig Engstrom and Dr Peter Friis.

Doctors should help patients achieve 150 minutes of moderate to vigorous exercise per week while those with unstable or multiple chronic conditions should be referred to a sports physician, the experts urged.