I'm a runner. Six days a week, every week of the year, I run between seven and 12 miles. Over 14 years ago, I was running seven days a week and I ended up with an ankle injury. It was devastating. I couldn't run for several weeks. Running is my sanity. Even though my wake-up call at 4:20 a.m. rarely leaves me feeling energized, I do zip out of bed because the way I feel after a run is well worth a little less sleep. Thus, those weeks were miserable. I read everything I could about how to quickly fix the injury and also turned to my father-in-law, a family physician and former runner. His advice was simple: "If you want to run for the rest of your life, you need to replace your shoes every 500 miles and you have to take one day off per week." I didn't love the advice, but I took it and have followed it ever since.