When my partner Catherine and I were in our fifties, we found out in short order that I needed a heart-valve replacement, and she had early-onset Alzheimer's. We both have a history as endurance athletes, so our reaction to this news was to sell our home, retire from our jobs, and become nomads, running marathons and half-marathons all over the world. My book Running All Over the World, adapted from a blog I wrote during our travels, is a nonfiction account of our five-plus years of flying, running, walking, sailing, and sightseeing from Atlanta to Antarctica and back again. Part travelogue and part-medical memoir, it transports readers to exotic places like Madagascar, Bhutan, and the Great Wall of China while at the same time offering a day-to-day look at what it means to have nothing but what's in your suitcase. It's also an offbeat love story, recounting the trials and tribulations of an ex-pilot with a passion for vistas and logistics and a woman so tough she walks a half-marathon in the Australian Outback mere weeks after breaking her ankle. During our years as nomads, we pushed our physical and mental limitations as often as we could-and we finished every race we ran hand in hand.