This paper presents current work on a pervasive health and fitness game (exergame), designed to motivate children to reach their recommended daily exercise goals and facilitate long term behavioural change. I discuss briefly the current work in the area of pervasive exergames and highlight a common theme in the approach they take. Through my study of the relevant psychology literature, I identify a potential problem in this approach - the goal context that the majority of systems adopt. I hypothesize that a `Task-Involved' rather than an `Ego-Involved' system would be more suitable at addressing the problem of sedentary childhood behaviour. Finally, this paper outlines the design requirements of a pervasive exergame with the aim of assessing whether one goal context proves more motivating than the other.