Exercise video games (exergames) can motivate players to be more physically active. However, most exergames are controlled by confined and predefined movements and do not promote long-term motivation. Well-funded commercial games often excel at long-term motivation, but are not operated with motion input. Exercise My Game (XMG) is a design framework for turning off-the-shelf action games into full-body motion-based games. Challenges with this approach involve finding mappings from control input to game-action, as well as blending active input feedback with the game’s interface. XMG facilitates transforming well-produced, non-exercise video games into captivating exergames by structuring the design space and outlining game requirements. We illustrate XMG with the example of turning the popular first-person action game Portal 2 into the exergame Sportal.