The article explores the power of fitness in recent American history. It argues that modern fitness is more than the physical condition to succeed in sports, but means having and shaping a body that stands for the willingness and ability to self-improvement, to lead a productive life, and to pursue happiness successfully. Today, a dynamic understanding of fitness seems self-evident, yet as the article argues, it is deeply embedded in modern history and in the shaping of societies based upon liberalism, self-government, and competition as their core principles. In order to come to terms with the climax of fitness in recent America, the article begins with a long-shot perspective on how a discourse revolving around an autonomous, liberal, and competitive self gained shape from the American Revolution to Charles Darwin, and how this sparked a dynamic understanding of fitness that became a most powerful, regulatory ideal of liberal societies. In a second step, the article zooms in on the beginnings of today’s fitness craze in the 1970s and 1980s in order to explore Major paradigms of the age of fitness in greater detail. The concept of ability is crucial to understanding the power of fitness, and examining the history of fitness is most important for a critical analysis of ableism.