Boston - When Dr. Michelle Johnson scribbles out prescriptions, the next stop for many of her patients is the gym, not the pharmacy.

Doctors treating chronic health problems increasingly are prescribing exercise for their patients — and encouraging them to think of physical activity as their new medication.

In one such program run by a health center in Boston’s Roxbury neighborhood, primary care physicians, internists and psychologists prescribe access to a gym for $10 a month, including free child care, classes and kids programs. Providing affordable gym access for patients ensures compliance, said Gibbs Saunders of Healthworks Community Fitness, a nonprofit gym in Dorchester that has partnered with several health care providers to help low-income residents fill their exercise prescriptions.

Executives at the Whittier Street Health Center say low-cost access to a gym is important, since many residents’ income is low and 70 percent of those they treat suffer from chronic problems such as obesity, high blood pressure, diabetes and depression.... Read More: VIN