This research is based on the finding that ergonomists experience professional difficulties impacting both on them and on their interventions. It is with this in mind that it aims to contribute to the enrichment of the initial training of the ergonomics of Quebec. To that end, the activity carried out by an ergonomist in an intervention situation during professional difficulties has been identified as the relevant research object. This activity is empirically studied on the basis of theoretical objects ± action courses’ and ± practical life courses’, offered by the semmiological framework of the action course (THEUREAU, 2006). An observatory consisting of observation data on the activity of an experienced ergonomist and verbal data relating to this activity has been implemented. The research produced two types of results. Empirical results take the form of three main categories of professional difficulties faced by the ergonomist, namely: (1) the active expectations of the ergonomist which have not been met; (2) contradiction between two or more commitments; (3) the limits of its benchmark. The nature of these difficulties is described, as is the activity carried out by the ergonomist. Technological results include benchmarks that can guide the development of devices to develop the ability to learn in action, an ergonomic competency framework, a description of the occurrence of activity-situation linkages typical of the profession that can be used in training and, finally, benchmarks for the development of aid modalities beyond training. The benefits of this research are threefold. From a technological point of view, it feeds into, but also goes beyond, the initial training of ergonomists, in particular by offering benchmarks for the development of support tools for practising practitioners. From an empirical point of view, the results provide a better insight into a hitherto little explored dimension of professional practice (ergonomics and professional practice in general), especially in terms of reflexivity and academic learning. Finally, from a methodological point of view, this research has made it possible to develop and test a system for studying professional practice over a long empan in a manner consistent with a holistic epistemology of human action.