The Effectiveness of a Functional Capacity Evaluation Among Persons on Sick Leave or Work Disability

The goal of this clinical trial is to evaluate Functional Capacity Evaluations in persons on sick leave or work disability. The main questions it aims to answer are: * What is the impact of FCE on the person on sick leave/work disability (quantitative) * What is the impact of FCE on the decision-making process by the medical advisor? (qualitative) * What is the usability, feasibility and quality of FCE for the medical advisor, occupational therapist, mediators of the regional services, and return-to-work coordinators? (qualitative) This is a randomized controlled trial (RCT). Participants in the control group will receive care-as-usual by the medical advisor. Participants in the intervention group will receive an FCE on top of care-as-usual. This is performed by an occupational therapist in their region, and a report of the FCE is delivered to the medical advisor. Both groups are asked to complete questionnaires at baseline, and after 3,6, and 9 months. Researchers will compare questionnaire results from participants in the control and intervention group, to see if their workability (primary outcome), steps to return to work, expectations to return to work, return to work beliefs, time until (partial) reintegration, self-efficacy in return to work, pain scale, and illness perception (secondary outcomes) are affected differently.