Digital motion-based games allow users to play computer games that are controlled with body movements. They can also be used as so called exer-games, purposefully combining exercises and games. Such computer games are a relatively new phenomenon. Low-cost tracking methods for game consoles allow for affordable full body tracking. Exergames have three major benefits. First, they can raise the motivation addressing the homo ludens and the immersion of interactive computer software can lead to a sustainable motivation for doing exercises. Second, they can give users feedback on doing physiologically positive movements and aggregate performance over time. Third, they can be customized (by adapting) to individual users. The latter is not only a great chance but also a great challenge in developing exergames. When employing exergames as games for health, e.g. in physiotherapy, many patients (users) have quite individual pre-dispositions, abilities and depending on the reason for their condition might have phases with more or less restrictions. Anticipating and adapting to physical ability and individual training goals on various time scales requires subtle mechanisms that capture differences between individual users over time. We present a structured analysis of the requirements of adaptivity, approaches for implementations, and argue for the introduction of antici-patory techniques in this context.