THE VALIDITY OF VISUAL OBSERVATION TO ASSESS POSTURE IN A LABORATORY-SIMULATED, MANUAL MATERIAL HANDLING TASK

A wide range of methods to evaluate posture in work situations relies on simple, unaided visual observation. In the present study the validi ty of visual observation to assess posture in a dynamic job was evalua ted. Postural aspects were observed and recorded during a manual mater ials handling job simulated in a laboratory. The results from these ob servations, concerning gross body posture, torso flexion, arms and leg s position, and load to be handled, were compared to the results obtai ned by direct opto-electronic recording. The agreement on a sample-to- sample basis (expressed by Cohen's kappa) was poor for the variables t orso flexion (mean value for kappa = 0.38), position of arms (kappa = 0.43) and legs (kappa = 0.46) and load to be handled (kappa = 0.50) an d acceptable only for the gross body posture (kappa = 0.79). Moreover, for each variable except gross body posture, the crude distributions of all observations and recordings across categories (irrespective of time) were significantly different. The results demonstrate that the o bservations are not valid. It is concluded that dynamic work situation s require less simple, more time consuming methods (e.g., analyzing fi lm or video records of the job) than a posture registration method bas ed on direct visual observation.