Every year, companies spend millions of euros for Work related musculoskeletal disorders (WMSDs). In order to reduce this cost and pain at work, they started to integrate Physical Assistance Device (PAD) such as exoskeletons. These new products aim to provide physical assistance to the operator but their integration is facing many barriers such as morphological adaptability, bad usability and a negative perception among workers. Exoskeletons are bringing a new type of interaction with human that is crucial to understand. This paper addresses the emerging issue of the impact of PAD on the hardness of manufacturing working tasks and on the usability satisfaction of workers. The use case focuses on a sanding operation on a catamaran hull, with an upper body passive exoskeleton provided by our partner Skel-ex. Experimental measurements such as cardiac cost, posture analysis and usability tests are carried out on a set of participants during finishing tasks. In order to better understand how exoskeletons support able-bodied people at work and reduce fatigue, we present results that show a positive impact of the assistance on physical workload