Comparison of the sensitivity of three psychophysical techniques to three manual materials handling task variables

The primary objective of the study was to determine the absolute and relati ve sensitivity of three psychophysical techniques of physical stress determ ination (Borg's Scale, the Visual Analogue Scale, and the Body Part Discomf ort Rating) in varied manual materials handling tasks. Ten young male and t en young female university students lifted a 22 kg box onto a shelf 132 cm high. The industrial-size box (40 x 20 x 20 cm) had two cut-out handles on the top middle of the two side panels. The shelf had restricted access allo wing 5 and 10 mm clearance for access. The palletizing was performed in sag ittal and 45 degrees asymmetrical postures under unlimited, 90% and 80% of stature headroom. The subjects lifted the box six times per minute for 5 mi n. After every lift the load was automatically delivered to the starting po sition. The 12 experimental conditions were randomized. Following each 5-mi n palletizing task the subjects were required to assess the immediately for egoing task on Borg's scale, the Visual Analogue scale, and a Body Part Dis comfort Rating scale. All data were subjected to statistical analysis inclu ding multivariate analysis of variance and Scheffe post-hoc multiple range test. Borg's scale was able to discriminate between two clearances, two sym metries and the three headrooms (p < 0.001). The Visual Analogue scale was able to differentiate between two symmetries and three headrooms (p<0.01), but the Body Part Discomfort Rating could not differentiate between any tas k conditions. Based on the study it is suggested that an appropriate match between the task demands and the basis of a psychophysical tool is essentia l for valid and reliable information.