Exergames are video games that require physically activity to play. In this talk, I will present research into the design of pedal-to-play games, where players use a recumbent bicycle to power their avatar in a game world. Our Liberi exergame has been designed to allow children with cerebral palsy to engage in physical activity, and combines a novel bicycle design with a set of action-oriented exergames that children can play from home over a network. I will report on testing of Liberi in both clinical and home settings, and also will report on the success of the game with typically-developing children. I will introduce the concept of “designing for exertion”, illustrating how exergames must be designed with physical activity in mind.