In this paper, we propose a dynamic difficulty adaptation approach for serious games dedicated to upper-limb rehabilitation after stroke. The proposed approach aims to provide a personalized rehabilitation session in which the training intensity and challenges can be adapted to patient's abilities and training needs. The objective is to increase the rehabilitation volume by getting the patient engaged to the therapy session. This approach has been implemented and tested through a point and click game. Finally, we present a pilot experiment that we have conducted with healthy people in order to explain how this approach has been implemented and integrated to post-stroke therapeutic games.