Musculoskeletal disorders (MSDs) are the leading occupational disease in France, Europe, and internationally. Due to challenging working conditions, care assistants in care homes for the elderly are particularly affected. Care professions are increasingly less attractive, while needs are growing due to the societal context of ageing population. Restoring leeway to healthcare professionals is a challenge to support their caregiving activities and prevent MSDs. We distinguish two types of leeway: Situational Operational Leeway (SOL) which is the workers' ability to implement an efficient operating mode in a working situation, and SocioTechnical Organizational Leeway (STOL) which is the possibilities the work environment offers to workers. This research aims to understand STOL, its link with regulations and SOL, and ways to support the creation of new opportunities, to sustainably prevent MSDs. To understand the perceived and actual STOL, we implemented a mixed quantitative and qualitative approach. The quantitative approach is based on data from a questionnaire aimed to identify and assess perceived STOL. The qualitative approach is based on work analysis aimed to identify the use of the available STOL during care activities. In an attempt to help increasing STOL, we carried out a participatory approach through collective confrontations and presentations. The quantitative approach partly predicts actual STOL and provided a valuable tool for conveying the reality to decision-makers and guiding the intervention. The qualitative analysis supplements the quantitative analysis. It reveals new dimension of STOL, in particular the STOL offered by the resident. It shows links between STOL and the possibilities for regulation, revealing potential levers for action. STOL offered by colleagues and by participatory setting are particularly important to regulate when faced to resident care difficulties. The care assistants' and management's analysis of real work situations allowed them to create new STOL with varying effects on the actors' activity. It seems that the link between STOL and development of SOL depends particularly on the existing work collective. STOL diagnosis could be a useful tool for guiding the intervention towards building the one that is favourable to regulations and development of SOL to prevent MSDs among care assistants. Keywords Leeway, Musculoskeletal disorders, care assistants, care homes for the elderly Context Despite efforts to prevent the risks in past years, musculoskeletal disorders (MSDs) are still the leading occupational disease in France, Europe, and internationally. The residential care homes for the elderly sector is particularly affected. In 2019 in France, 94% of recognised occupational diseases were linked to MSDs 1 .