Evaluation of perceived discomfort in repetitive arm reaching and holding tasks

This study investigates the effect of arm reaching and holding related factors on subjective discomfort rating. Fifteen males and fifteen females participated in the experiment. Independent variables include shoulder flexion (60°, 90° and 120°), reaching frequency (2 motions/min and 4 motions/min), holding weight (0.86 kg and 1.12 kg), and holding duration (5 s and 10 s). The response measures include subjective discomfort ratings of the whole body (WBD), shoulder (SD) and upper arm (UAD). The ANOVA results indicate that the effects of gender, shoulder flexion, reaching frequency, holding weight, and holding duration significantly influence all measures. Findings also show significant positive correlations among WBD, SD and UAD. Arm reaching over shoulder height is the main factor affecting WBD for both males and females. Further, the high frequency of arm reaching shows greater influence on female participant's WBD than other factors. On the other hand, holding weight shows greater influence on male participant's WBD than other factors. Moreover, this work constructs nine regression models to predict WBD, SD and UAD from arm reaching and holding related factors. The discomfort prediction models explain at least two-thirds of the variations. Relevance to industry: This study evaluates the effects of shoulder flexion, reaching frequency, holding weight, and holding duration on whole body and body part discomfort. The findings of this study can be used for job and workplace design.