In 2007, Anne Mahlum was living in Philadelphia. She had a habit of waking up early to exercise; each morning, her route took her by a homeless shelter. Even at dawn, there were people out in front. One morning, they waved. As Mahlum built up a rapport with her early-morning neighbors, she started thinking: Why am I running past them when I could run with them?

Mahlum had started running as a teenager to cope with troubles at home. Maybe, she thought, running could help other people the same way it did her?

[For more of this story, written by Eillie Anzilotti, go to http://www.citylab.com/cityfix...an-francisco/488522/]