Abstract : The growing number of musculoskeletal disorders in industry could be addressed by the use of collaborative robots, which allow the joint manipulation of objects by both a robot and a person. Designing these robots requires to assess the ergonomic benefit they offer. Current methods use a posteriori assessment, i.e. observation of the worker, and need a physical mock-up of the robot. Moreover, they exclude dynamic phenomena because their measurements require heavy instrumentation. It has been proposed to use a digital human model, allowing to assess the ergonomic performance of a collaborative robot during the design process. This paper presents preliminary results on three ergonomic indicators formulated to meet the requirements of collaborative robotics. They evaluate respectively the position of the worker, his physical effort and the energy spent during the task. The same manual task is performed by seven human subjects under different time, load and geometric constraints. Each performance is recorded and replayed with a digital manikin in a dynamic simulation framework, in order to calculate the values of the indicators. All three indicators are strongly affected by the geometric parameters in a way that is consistent with ergonomic guidelines. Besides, a linear correlation between the values of the indicators and the penibility perceived by the subjects is observed. Moreover, the results show that the relevance of an indicator is strongly affected by the task features, especially its duration. Future work will be directed towards automatic selection of relevant indicators for a given task.