How would your performance change if you were at your optimal body weight? Imagine what it would feel like to set out on a run weighing 10 pounds less than you do right now. How much would it affect your efficiency, your endurance, or more simply, your self-image?

When was the last time you saw a marked improvement in your fitness? Do a few extra pounds stand between you and a faster race? Chances are it was your quest for optimal body weight that led you to pick up Racing Weight.

When I was almost done writing this book I received an e-mail, in my capacity as content director of Competitor Running, from Darwin Fogt, a Los Angeles–based physical therapist, who invited me to stop by his facility at my convenience and try out his Alter-G antigravity treadmill. I had been dying to step onto one of these machines since I first heard about them a couple of years earlier, so I readily accepted his offer.

The Alter-G allows the user to walk or run at the equivalent of as little as 20 percent of his or her body weight by increasing the air pressure within an airtight tent that seals around the user’s waist and thereby lifts the runner. Many elite runners, including two-time Olympian Dathan Ritzenhein, use it to train through injuries that prevent them from running on their full body weight. Others, such as NCAA champion Galen Rupp, use it to increase their running volume without increasing their risk of injury.

My epiphany came when Fogt zipped me into his Alter-G, increased the belt speed to my normal jogging pace, and then reduced my effective body weight to 90 percent. Instantly I felt as if I had become 10 percent fitter. Scooting along at a 7:00/mile pace was utterly efortless. It was not a feeling of gross artificial assistance, like running on the moon. Rather, it felt like normal running, only so much better.

While I was motivated to write this book by a belief that body-weight management is critical to performance in endurance sports, I don’t think I fully appreciated it until I efectively lost 15.5 pounds instantaneously on the Alter-G. It was a stunning lesson. I left Fogt’s facility feeling twice the sense of urgency about spreading the messages of this book as I had felt when I started writing it.

Another motivation for writing this book was my awareness that many endurance athletes struggle to manage their body weight effectively and frequently go about it all wrong. Some of the most extreme examples are to be found in the elite ranks, where money and glory are at stake. In the 2005 documentary film What It Takes, three-time Hawaii Ironman world champion triathlete Peter Reid confessed to going to bed so hungry that he suffered from headaches during periods when he was trying to lose weight. In 2008, world champion cyclist Marta Bastianelli of Italy was banned from competition after one of her blood samples tested positive for an illegal diet drug. Bastianelli admitted that she took the drug after receiving pressure to lose weight from her coaches.

As these examples indicate, professional endurance athletes know that controlling their body weight and body fat is critical to achieving maximum performance, but reaching optimal race weight never requires an athlete to go to bed hungry or take illegal diet drugs.

It’s not just the pros who worry about getting leaner and are confused about the best way to do so. Recently I assisted exercise scientists from Montana State University in conducting a survey of endurance athletes concerning their attitudes about their body weight and their weight-management practices. More than three thousand cyclists, runners, triathletes, and other endurance athletes responded. Most were serious competitive athletes who trained at least one hour a day, five days a week. The results of the survey, which were presented at a meeting of the Society for Behavioral  Medicine in Montreal, Canada and published in the Annals of Behavioral Medicine (Ciccolo et al. 2009), were quite interesting.