This paper is a study of the aspects that are important to consider when designing an unobtrusive interaction for wearable devices in the area of extreme sports. The work is based on an analytical study of seemly-unrelated areas with the common facet that they all call for an unobtrusive interaction in their devices. The findings of the analysis conclude that it is necessary a change of direction in the design because it is not possible to design an unobtrusive interaction that relies on active manipulation. Activity theory and affective computing present theoretical principles with the potential to be used as a framework for HCI and solve the mentioned issues. Finally, I design the user interface of a specific case in the areas of mountain biking and skiing to use it as design-oriented research. An essential aspect of this case is the use of expert feedback and video simulations to drive the design process. Another important point is the definition of the situations and variables that will be observed by the system to adapt itself so it is able to continue being unobtrusive and helpful through the changes.