Musculoskeletal disorders (MSDs) are the most widespread work-related health problems in the European Union, all professional sectors combined (de Kock & al., 2019). Faced with these risks, training has a role to play as an essential prerequisite for the implementation of sustainable prevention actions (Caroly & al., 2008). Unfortunately, most MSD prevention training struggles to produce satisfactory effects. They aim to ensure that professionals adopt safety techniques or "good gestures and good postures" developed to achieve maximum efficiency with minimum motor cost. But these safety techniques do not take into account the diversity and variability of work situations and they cannot always be respected (Denis & al., 2013; Denis & al., 2018).

One of the potential ways of improving this prevention training lies in training that would allow trainees to identify the characteristics of risky situations as well as the means of preventing them (Verdier, 2010). To this end, the video offers the possibility of observing and analyzing work situations to both identify the risks and to collectively discuss the resources to be deployed in the activity to prevent these risks, such as know-how prudence or efficient know-how that target joint prevention and performance objectives (Ouellet & Vezina, 2009).

However, this type of video training requires trainers to transform their activity. Indeed, for trainers who have not received training as trainers and who prescribe to their trainees a single operating procedure for each gesture, which must be precisely respected, integrating MSD prevention into their teaching requires them to appropriate new training content oriented towards risk prevention, being able to lead discussions based on videos about advantages and disadvantages of the different operating procedures for performance and prevention, and finally, being able to approach the variability of these operating procedures as a means of preventing MSD risks without neglecting performance.

As part of a process of designing videos for saddler-harnessers training that integrate musculoskeletal disorder risk prevention (Body & al., 2020; Body, 2022), our proposal aims to show how a collaborative and iterative process based on the articulation of a variety of interview techniques bringing together saddler-trainers with different levels of experience and expertise in the trade, enables these professionals to transform their representations of the etiology of MSDs, their relationship to pain at work and in training, and their activity as trainers.

Our corpus is made up of transcripts of individual self-confrontation, collective allo-confrontation interviews (Mollo & Falzon, 2004) and co-explanation interviews (Vinatier, 2010) conducted throughout the video design process. Depending on the techniques and the moments of the process, they brought together groups of 3 to 13 saddler-trainers composed of beginners, experienced people and experts. These interview techniques are known to allow the researcher to identify the content of the work and the knowledge mobilized to accomplish it, but also to have formative effects. They facilitate awareness of the knowledge mobilized in the action, putting it into words and the construction of collective knowledge (Mollo & Falzon, 2004) or to allow the acceptability of practices to be judged within the collectives (Nascimento & Falzon, 2014).To identify these formative effects, these transcripts were analyzed with a clinical approach (Clot & Leplat, 2005; Rochex, 2010). The categories of analysis, constructed as the analysis progressed, are organized around questions of health at work and in training: origins of MSDs, relationship to pain, criteria for observing the implementation of professional gestures, possibilities for action by trainers to prevent risks.

The results of our analyses show that the transformations in the representations of saddler-trainers concern several objects. First of all, they concern the recognition of the phenomenon of MSDs as an occupational disease, which also concerns saddler-trainers and not only professionals subject to the carrying of heavy loads. Thus, transformations in the representations of the etiology of these disorders are also present. From a representation centered exclusively on biomechanical factors (repetition of movements, force to be applied), the saddler-trainers integrate psychological factors such as well-being at work. The relationship with pain is also changing for some. Initially seen as an obligatory part of learning the saddler's gestures, pain is now considered as a warning sign of the risk of MSDs, especially if it persists beyond the initial training period. Finally, the saddler-trainers also project themselves into a training model that is less focused on the transmission of a single operating procedure. They see their role as mediators who can use the video as a space for developing the trainees' reflexivity about their postures and movements to promote the conceptualization of the action.

Body, G. (2022). Conception de vidéoformation pour le développement des gestes professionnels : une approche de didactique professionnelle. [thèse de doctorat, Nantes Université]. Thèse.fr https://www.theses.fr/2022NANU2019 Body, G., Vidal-Gomel, C. & Simonet, P. (2020). Engagement du corps et prévention des troubles musculosquelettiques dans la co-conception d’une formation initiale au métier de sellier. Les Sciences de l'éducation - Pour l'Ère nouvelle, 53, 77-102. https://doi.org/10.3917/lsdle.534.0077 Caroly, S., Coutarel, F., Escriva, E., Roquelaure, Y., Schweitzer, J.M., & Daniellou, F. (2008). La prévention durable des TMS : Quels freins ? Quels leviers d’action ?. PACTE ; ANACT ; LEEST ; Equipe d’Ergonomie Bordeaux. https://halshs.archives-ouvertes.fr/halshs-00373778/ Clot, Y. & Leplat, J. (2005). La méthode clinique en ergonomie et en psychologie du travail. Le travail humain, 68(4), 289-316. https://doi.org/10.3917/th.684.0289 Denis, D., Lortie, M., Plamondon, A., St-Vincent, M., Gonella, M., & Irsst, G. (2013). Proposition d'une définition de la compétence en manutention et impacts sur la formation. Le travail humain, 76(2), 129-153. https://doi.org/10.3917/th.762.0129 Denis, D., Gonella, M., Comeau, M., & Lauzier, M. (2018a). Pour quelles raisons la formation aux techniques sécuritaires ne fonctionne-t-elle pas ? Revue critique de littérature. (R-1013). IRSST. https://www.irsst.qc.ca/publications-et-outils/publication/i/100981/n/raisons-formation-techniques-securitaires-manutention-revue-critique-litterature de Kock, J., Vroonhof, P., Snijders, J., Roullis, G. Clarke, M., Peereboom, K., van Dorst, P. & Isusi, I. (2019). Work-related musculoskeletal disorders: prevalence, costs and demographics in the EU. (ISSN: 1831-9343). European agency for safety and health at work. https://osha.europa.eu/en/publications/msds-facts-and-figures-overview-prevalence-costs-and-demographics-msds-europe Mollo, V., & Falzon, P. (2004). Auto-and allo-confrontation as tools for reflective activities. Applied ergonomics, 35(6), 531-540. http://dx.doi.org/10.1016/j.apergo.2004.06.003 Nascimento, A., & Falzon, P. (2014). Jugement différentiel d'acceptabilité et cultures de sécurité en radiothérapie. Le travail humain, 77(4), 325-349. https://doi.org/10.3917/th.774.0325 Ouellet, S., & Vézina, N. (2009). Savoirs professionnels et prévention des TMS: portrait de leur transmission durant la formation et perspectives d’intervention. Perspectives interdisciplinaires sur le travail et la santé, 11(2), 1-42. https://doi.org/10.4000/pistes.2251 Rochex, J. Y. (2010). Approches cliniques et recherche en éducation. Questions théoriques et considérations sociales. Recherche et formation, 65, 111-122. https://journals.openedition.org/rechercheformation/165 Verdier, E. (2010). Petites entreprises et jeunes salariés de la réparation automobile : le rôle de la formation initiale dans la prévention des risques professionnels. Formation Emploi, 111, 67-83. https://doi.org/10.4000/formationemploi.3111 Vinatier, I. (2010). L’entretien de co-explicitation entre chercheur et enseignants : une voie d’émergence et d’expression du « sujet capable ». Recherches en éducation, Hors-série n°1, 111-229. http://www.recherches-en-education.net/IMG/pdf/REE-HS-no1.pdf#page=111