To stretch or not to stretch? That is the question. When you stretch, you are increasing your flexibility and improving the motion of your muscles and joints. But when it comes to running, is stretching absolutely necessary?

We talked with two-time Olympic coach Gale Bernhardt, a leading athletic trainer and co-author of Become a Fat-Burning Machine, to find out what runners need to know about stretching.

Women’s Running: Is it best to stretch before or after a run?

Gale Bernhardt: It is best to stretch muscles after a warm-up or at the end of your run. If you decide to stretch after your warm-up and before the main set of your run, know research has shown that stretching alters the workout. The alteration is reduced power.

WR: Is it necessary to stretch after a run?

GB: Some runners—and we don’t know why—don’t seem to benefit from stretching. Others, who are prone to injuries related to limited range of motion, do seem to benefit.

WR: What muscles, if any, should you focus on stretching?

GB: The major muscle groups used in running include the hamstring, calf, quadriceps and the glutes. Most runners that do stretch should focus on these muscle groups.

WR: What about foam rolling? Is that necessary?

GB: Similar to stretching, foam rolling comes with controversy. It seems to help some people but not all. If you are a person that finds foam rolling beneficial, keep it up. If foam rolling doesn’t seem to help—or worse yet, it seems to cause you more problems—cut it from your routine for a while to see if you notice a difference.