DEAR MAYO CLINIC: My grandmother lives with me, and she is always nagging me to "stand up straight" and "put your shoulders back." She says good posture will keep me healthy as I age. But I'm only 17.

We’ve all seen it, whether in other runners or in our own race photos: the high hip, knocked knees, a sort of bobbing gait that looks inefficient and downright uncomfortable. To the untrained eye, it ...