MECHANICAL-BEHAVIOR AND STRENGTH OF THE MOTION SEGMENT UNDER COMPRESSION - IMPLICATIONS FOR THE EVALUATION OF PHYSICAL WORK LOAD

It has been shown that the energy storage in motion segments under compression, which is dependent on the temporal pattern of the force applied, is a good predictor of the occurrence of damage. In the present paper two case-studies are described in which energy storage is calculated to evaluate work load. In the first case-study job-rotation, a change of the temporal characteristics of the work load appears to cause a decrease of the energy stored and hence of the risk of damage. In a case-study on lifting it is shown that the effect of a reduction of the intensity of the work load (i.e. a reduction of the mass lifted), can be offset by changes of the frequency or duration of lifting. These adverse effects of the change in frequency or duration are not adequately reflected in the NIOSH lifting guidelines. It is concluded that temporal characteristics have to be considered when evaluating work load and that the calculation of energy storage in the motion segment can be used to this end.