We have developed a collection of portable platforms to enable context-aware applications to help users with their personal fitness. Our approach has been to focus on established form-factors such as cellphones and wrist-watches for the user interfaces. A variety of sensors are used to infer aspects of the user's context and proactively gather and display information that is likely to be useful at that time. In this paper, we highlight some of our platforms, the roles they can play, some of the capabilities we have already implemented, and highlight some of the applications we are currently developing.