Effect of external load at varying hand positions on perceived discomfort.

The purpose of this study was to assess the effect of external load at varying hand positions on discomfort, and to provide a new classification of external load. An experiment was carried out in which 16 postures with an external load of 0, 1.5, 3 kg were tested. The postures were controlled by 2 independent variables of hand distance and hand height. The subjects were instructed to rate their perceived discomfort with magnitude estimation after holding a given posture for 1 min. Analysis of variance (ANOVA) exhibited that the main effects of the 3 independent variables were statistically significant for discomfort. Discomfort increased linearly with external load and hand distance. Hand height showed a quadratic relation with discomfort, which exhibited a slightly different trend from hand distance and external load. Based on the results, a new classification of external load was proposed with 3 classes grouped by perceived discomfort.