Joe Henderson, the first editor of Runner’s World, and Joan Ullyot, M.D., author of three women’s running books, first popularized the 10-percent prescription in the 1980s. “I noticed that runners who increased their training load too quickly were incurring injuries,” says Dr. Ullyot.

In my own personal experience, I’m seeing this play out.  I recently decided to add some extra training to my regimen.  So I poured it on during my next workout.  I powered through that workout and loved every second of it.  In fact, I loved it so much that I decided I must be the Exception to the Rule.  What happened next?

That night, as I was standing in my kitchen working on a lovely sweet treat, I experienced the nastiest cramp in my foot.  It was in a joint muscle in one of my toes.  That nasty workout-stealing leeching (this is probably slandering the leeches of the world) charlie horse took hold of my left foot and didn’t let go for hours.  Hours and hours.