Assessment of mechanical exposure in ergonomic epidemiology

In recent years several different methods have been developed to assess mechanical exposures, which are related to musculoskeletal disorders in ergonomic epidemiology. Each of these methods is capable of measuring one or more aspects of risk factors, but has drawbacks as well. Improper application of methods might result in biased exposure estimates, which has serious consequences for risk estimates arising from epidemiological studies. The aim of this paper was to systematically evaluate the usefulness of different measurement methods in terms of accuracy and applicability. Assessment of external exposure measures by subjective judgements (from experts or self reports from workers), observational methods (on site or afterwards from video recordings), and direct measurements methods (at work or during laboratory simulations) are discussed for each of the dimensions of exposure level, duration, and frequency. It is concluded that expert judgements and self reports give only limited insight into the occurrence of tasks and activities. Further information can be obtained from observations, which can best be combined with direct measurements of exposure to posture, movement, and exerted forces to achieve exposure profiles by occupational task. Internal exposures estimated by biomechanical modelling mostly consider the low back and require information on postures of the different body segments and exerted forces, completed with movement data in the case of dynamic models. Moreover, electromyography (EMG) and measurements of intra-abdominal pressure might be used for this purpose. Both biomechanical models and EMG are useful methods to assess internal exposure, but biomechanical models should not be restricted to the level of compressive forces on the lower back. Finally, current problems and future directions in measurement strategies and methods are discussed.