Exertion games require investing physical effort. The fact that such games can support physical health is tempered by our limited understanding of how to design for engaging exertion experiences. This paper introduces the Exertion Framework as a way to think and talk about Exertion Games, both for their formative design and summative analysis. Our Exertion Framework is based on the ways in which we can conceive of the body investing in game-directed exertion, supported by four perspectives on the body (the Responding Body, Moving Body, Sensing Body and Relating Body) and three perspectives on gaming (rules, play and context). The paper illustrates how this framework was derived from prior systems and theory, and presents a case study of how it has been used to inspire novel exertion interactions.