REduction of the lifting Load Among logistics workers through a passive back eXoskeleton. Protocol of the RELAX project, an 18-month in-field controlled intervention study

Background Occupational exoskeletons are used to reduce physical workload and prevent work-related musculoskeletal disorders in physically demanding jobs. Although laboratory studies demonstrate reduced muscle load during simulated manual work tasks, evidence from long-term, real-world implementations remains very limited. The RELAX project aims to investigate the long-term effects of a passive back-support exoskeleton (BSE) during manual order-picking work in a Danish warehouse, focusing on health and socio-economic outcomes. Methods This 18-month controlled in-field intervention study compares outcomes at two warehouse departments: one where workers use a passive BSE and a control group where workers perform work tasks as usual. Approximately 90 full-time workers will be followed during the intervention period with questionnaires, interviews and company-registered performance indicators. Primary outcomes include perceived work intensity and musculoskeletal discomfort, while secondary outcomes include sickness absence, employee turnover, productivity and cost effectiveness. Furthermore, a process evaluation will be conducted based on questionnaires, focus-group interviews, and reported exoskeleton use. Quantitative effects will be analysed using difference-in-difference analysis with generalized linear mixed models to account for repeated measures over time. Employee turnover will be analysed using time-to-event analysis, and qualitative focus-group interviews will be analysed using reflexive thematic analysis to explore implementation processes and contextual factors. Cost-effectiveness and return on investment will be assessed by comparing the investment with potential savings in costs and resource use. Discussion By combining longitudinal quantitative outcomes with qualitative process evaluation, the study seeks to provide ecologically valid evidence on the effectiveness, feasibility and sustainability of occupational exoskeleton implementation. This approach will help clarify whether long-term exoskeleton use improves worker health without compromising productivity and may inform future workplace guidelines and large-scale adoption strategies.