But what should you stretch? "The main muscles and muscle groups worked when you run are the quads, hamstrings, calves, hip flexors, and glutes," says Rachel Mariotti , a Tier III+ personal trainer and Precision Running Coach at Equinox. Your running routine should ideally be flanked by two stretch sessions: dynamic or moving stretches pre-run, and static or holding stretches afterwards, she says. In a perfect world, you'd also add some strength training and yoga into your workout routine to vary things up, but that's not always doable, so stretching it is. "The impact of running is very high, so strong muscular support is needed for your joints," Mariotti says.