By Amanda Loudin, Special To The Washington Post Samantha Strong knows stress fractures. A former collegiate triathlete and high school runner, the 22-year old graduate student estimates she had eight or nine over her high school and college careers. Each one, she says, took longer than the last to heal. “My first stress fracture was in my tibia, and I was told it would take about six weeks to heal,” says Strong, who lives in Arlington, Va.