Prof. Willem van Mechelen has a unique combined background in physical education, human movement sciences, epidemiology, (occupational and sports) medicine and public health/primary care. After a career as classroom physical education teacher and occupational physician, he completed his PhD at age 40 years. From that time onwards he engaged himself seriously in science. His research group, which he has built up from scratch in the past 20+ years, has an international reputation and a leading position in the two fields of social medicine he represents: occupational medicine and public health/sports medicine. In Occupational Medicine he has evaluated and introduced graded-exercise programs as highly cost-effective means for return-to-work of workers on sick leave, as well as worksite lifestyle interventions for the entire workforce.