Does running build muscle?

Running won't help a person build big, strong muscles. A key reason is that running shrinks certain muscle fibers. The fibers, known as type II fibers, make up about half the body's muscle fibers that have growth potential.

To build muscle, the body needs a calorie surplus because it converts the extra calories to muscle. Running, if done too frequently or too long, can cause a calorie deficit, especially for someone on a 2,000 calorie-a-day diet. This can cause the body to react by putting the person in starvation mode, and by actually eating away at the muscle, instead of building it up.