Running is one of my favorite ways to sweat, but there is a dark side to my healthy exercise habit: I don’t stretch! This makes me prone to tight legs, achy joints, and a nagging pain in my left hip.

When it comes to stretching out your muscles, there are a lot of options to choose from. To boil it down, we turned to Marilyn Moffat, a professor of physical therapy at New York University and the ...