Measurement and evaluation of postural load in occupational work situations

This paper describes methodological considerations and problems experienced when quantifying muscle load in occupational work situations. A system for the quantification of the health effect of prolonged muscle load on the shoulder muscles is also described. Combined measurements of postural load and health effects can be used in a quantitative evaluation of postural load as a risk factor for the development of musculo-skeletal injury. Postural muscle load may be quantified by electromyography or by biomechanical methods. Problems associated with quantitative electromyography are described, including selective inhibition of functional compartments in a muscle. This phenomenon results in other compartments coming under proportionally higher strain, disturbing the force-EMG calibration curves. It is suggested that fatigue measurements, indicated by a shift in the centre frequency of the EMG frequency spectrum, are not easily used for evaluation of vocational EMG recordings if the purpose is to indicate the risk of occupational muscle injury. Load measurements using biomechanical methods may provide an acceptable alternative to electromyography, but more work is required before these methods can be used on a routine basis.