Despite the fact that physical activity is universally acknowledged to be an important part of healthy functioning and well-being, the full scope of its value is rarely appreciated. This article introduces a novel framework for understanding the relationships between physical activity (and specifically sport-related forms of physical activity) and different aspects of human development. It proposes that the outcomes of physical activity can be framed as differential 'capitals' that represent investments in domain-specific assets: Emotional, Financial, Individual, Intellectual, Physical, and Social. These investments, especially when made early in the life course, can yield significant rewards, both at that time and for years to come. The paper presents a new model-the Human Capital Model-that makes sense of these effects, outlines the different capitals, and briefly articulates the conditions necessary for the realization of Human Capital growth through physical activity.