Abstract
Cumulative trauma disorders (CTDs) have a great impact on the health and safety of workers. By using subjective discomfort rating to evaluate workload, improper designs of work can be improved. It can both prevent workers from CTD of the upper limbs and enhance job satisfactions. In the experiment, we considered the combination of holding height (shoulder height, hand heights of flexion and extension 30o from shoulder height), load (0.86 kg and 1.12 kg), frequency (2 times/min. and 4 times/min.) and duration (5 sec. and 10 sec.) of motion to simulate the 48 holding tasks. Fifteen male and fifteen female voluntary subjects executed each experiment condition for 60 seconds, then conducted discomfort ratings of whole body and local body parts. At the same time, rapid upper-limb assessment (RULA), EMG, range of joints motion and speed of motion were collected to compare with the discomfort ratings. The results of the analysis of discomfort ratings showed that male subjects differed significantly from female subjects. The male subjects had the highest discomfort feeling in target height over shoulder, but the female subjects in high frequency of motion. For the constructed discomfort prediction models for holding tasks, the coefficients of determination (R2) for males and for females were 0.7 and 0.76. The models can provide a convenient and efficient tool to predict one’s subjective discomfort with the parameters including holding height and distance, load, frequency and duration time.