Assessment of postural load for lower limb postures based on perceived discomfort

For evaluating postural loads, leg postures are usually considered to be less important than postures in other body parts, such as arms, shoulders, and trunk. Leg postures are yet closely related to postural stability and their influence on the whole-body postural load should be fully reflected in evaluating postural stresses. In this study, 31 leg postures were evaluated based on a subjective discomfort rating. Eighteen male subjects were asked to maintain a series of leg postures for 1 min, and to report their perceived discomfort using a free-modulus magnitude estimation method. Results showed that leg posture had a significant effect on the subjective discomfort rating. The results led to the development of a preliminary postural classification scheme, in which leg postures were classified into 6 categories (standing, knee-flexion, squatting, sitting, kneeling, and one-foot posture) followed by 10 sub-categories. A relative discomfort score on a ratio scale was assigned to each category, which was based on a normalized discomfort value for sitting. This ratio discomfort score is useful to quantitatively evaluate postural loads for a variety of leg postures, and to compare them across different leg postures. Postural loads of leg postures were quantified using the psychophysical method. The result of this study will provide the basis to evaluate leg postures adopted by workers in various jobs.