Running is one of the most accessible forms of exercise: Lace up your sneakers and go. And 5Ks are one of the easiest options for toeing your way into the racing world. The thing is, you can run 3 miles a day for weeks —even months — and still be surprised on race day. I sure was. While I was an elite athlete, I was a skier and had to avoid running in general when I was training since all of the pounding can be a little rough on already-sensitive knees. But now that I’ve reti