EVALUATION OF PERCEIVED AND SELF-REPORTED MANUAL FORCES EXERTED IN OCCUPATIONAL MATERIALS HANDLING

The main objective of the study was to evaluate the ability of workers to reproduce simulated manual work forces correctly and to quantify t hese forces in Newtons (N) by means of self-reports, Fourteen male and 14 female workers participated in the study, Three experiments were c arried out, In the first experiment, the ability to reproduce the magn itudes of simulated manual forces occurring in daily work and to estim ate these forces in Newtons was tested, A specially designed force-mea suring device was used for this purpose. In the second experiment, the subjects estimated the weights of five boxes ranging from 1 to 30 kg. In the third experiment, the subjects were asked to produce five pred etermined push and pull forces ranging in magnitude from 10 to 300 N o n to the handle of the force-measuring device. The ability to reproduc e the magnitudes of manual forces when simulating four familiar work t asks was good (the intraclass correlation coefficients ranged from 0.7 5 to 0.95). The ability to quantify these forces in Newtons was not as good (the product moment correlation coefficients ranged from 0.21 to 0.69). When the subjects estimated the weights of boxes they underest imated the weights. When they produced predetermined push and pull for ces they exerted higher forces than expected when low force levels wer e requested, and lower forces when high force levels were requested, H owever, the forces were correctly ranked. In summary, simulation of th e manual push/pull forces used in familiar work tasks seemed to offer sufficient reproducibility to be worth testing for validity. Self-repo rts, used without previous training or without known 'reference forces ', seemed to be very rough when the aim was to estimate in kg or Newto ns. However, the fact that individuals could rank the forces correctly opens a potential for refinement of self-reports as a method for quan tifying manual forces in objective terms, e.g. kg or Newtons. Copyrigh t (C) 1996 Elsevier Science Ltd.