This communication aims to show why guidelines to prevent discomfort of static postures can be based on endurance data, and to give insight in the aim and scope of a recent 'work-rest model for static postures' (WR model). The paper is a response to a recent paper of Mathiassen and Winkel (1992) who questioned the usefulness of discomfort and endurance data, and of the WR model for developing guidelines for static postures. It is concluded that discomfort can be considered as an independent evaluation variable for working postures, anchored in European legislation. Discomfort can be predicted from the 'remaining endurance capacity' (REC) because of a known relationship between the REC and discomfort as measured with the Borg rating scale. The WR model estimates at group level the mean REC of a static posture with or without an external force during and immediately after a work-rest schedule. The WR model is meant to assist practitioners in the assessment and optimization of static postures (and external forces) and work-rest schedules in order to avoid high levels of discomfort.