[Why do musculo-skeletal stress injuries increase?]

The innovation of technologies in the industrial countries in recent decades has involved increased physical monotony and inactivity in working life. Parallel to this development the ergonomic quality of work station design has been improved. But the corresponding reduction in physical stress does not seem to diminish the frequency of symptoms from the locomotor system. On the basis of studies carried out in recent years, a U-shaped relationship between physical stress and symptoms is suggested, i.e. frequency of symptoms may increase not only when the physical stress is high but also when it becomes very low. It is concluded that further research on acceptable physical stress should comprise studies aimed not only at upper but also at lower limits, including minimal variation of the physical load.