Complete and unambiguous descriptions of user tasks is a cornerstone of user centered design approaches as they provide a unique way of describing precisely and entirely users’ actions that have to be performed in order for them to reach their goals and perform their work. Three key challenges in describing these user tasks lay in the quantity and type of information to embed, the level of details of the type of actions and the level of refinement in the hierarchy of tasks. For “standard” interactions, such as performing work using desktop-like interactive applications, several notations have been proposed and make explicit how to address these challenges. Interactions on the move raise additional issues as physical movement of the operator have to be accounted for and described. Currently no task notation is able to describe adequately users’ movements making it impossible to reason about quantity of movement to perform a task and about the issues for performing incorrect movements. This paper extends current knowledge and practice in tasks modelling taking into account in a systematic manner users’ movements and more precisely body parts, body size, range of motion, articulations and position of body parts relatively to objects in the environment. Through two different case studies we show the importance of adding those elements to describe and analyze users’ work and tasks when users perform physical interactions. We also demonstrate that such models are of prime importance to reason about quantity of movements, muscular fatigue and safety.