Runner's Quads

I am curious as to what i have labelled 'Runner's Quads', I am referring to the sagging vastus medialis of endurance runners. Does anybody know of the reasoning why this happens? And what can be done to stop/prevent it, as I am starting to develop it?

Ed

By sagging vastus medialis do you mean a loss of muscle tone or the development of a more pronounced musculature?

Yours in Fitness,

Coach Sommer

Do you run by pulling or pushing?