The arena of sport is filled with marvelous performances and feats that, at times, seem almost beyond belief. As curious onlookers, we often wonder whether or not athletes will reach certain peaks and what determines their limits of athletic performance. Science, with its emphasis on theoretical development and experimental results, is uniquely equipped to answer these kinds of questions. Over the past two decades, I have been asked innumerable questions related to how science can provide these kinds of insights. Science in the Arena is written as an outgrowth of those interactions with the primary goal of communicating useful and understandable scientific explanations of athletic performance.