Abstract
This dissertation aims to evaluate the effect of prolonged walking task for lower limb and arm reaching and holding task for upper limb on whole body and body part discomfort ratings. The first experiment evaluates the significance of boot sole properties on reducing fatigue, and the effect of load carrying and one hour walking based on biomechanical, physiological and psychophysical responses, and further to investigate the correlations of the measurement methods. The results indicated that elasticity and shock absorption of the boot showed significant effects on outcome variables. Significant load effects can be seen in most measurements except two measures: hip joint angle and front thigh discomfort. All of the significant period effects gave strong regressions, with no R2 value less than 98.3%, all p<0.001. The second experiment evaluates the effect of shoulder flexion angle, weight load, task frequency, and duration on subject’s perceived discomfort. The response measures include discomfort ratings of whole body and local body parts, and the EMG of biceps brachii, anterior deltoid, upper trapezius and flexor digitorum. The results indicate that the effect of reaching height, reaching frequency, load weight, and holding duration were significant on most of the response measures. Arm reaching over shoulder height was the main factor affecting whole body discomfort for both males and females. Further, the high frequency of arm reaching showed greater influence on female subject’s discomfort rating than the other factors. The holding weight showed greater influence on male subject’s discomfort rating than the other factors. Moreover, six regression models were constructed to predict the whole body discomfort feelings from the arm reaching and holding related factors. At least two-third of the variation can be explained by the discomfort prediction models. Furthermore, the development of discomfort prediction models can help to build motion prediction of digital human model and to improve workplace design.