CHICAGO (AP) — Three times a week, Rita Driscoll steps onto a treadmill at a Minnesota hospital under the eye of a rehab therapist. She walks until it hurts — pushing her limits, walking faster and adding steeper inclines.

The retired school aide has leg pain caused by clogged blood vessels. Until recently, monitored walking wasn't an option for people with peripheral artery disease, or PAD, because most insurance doesn't cover it.

"I'm not giving up my legs," said Driscoll, who walks as part of a study. "Hopefully it will keep me away from surgery and keep me walking and dancing."

Medicare ha...