The boundaries for joint angles of isocomfort for sitting and standing males based on perceived comfort of static joint postures

This study presents data for the joint angles of isocomfort (JAI) in sittin g and standing males based on perceived comfort ratings for static joint po stures maintained for 60 s. The JAI value was defined as a boundary indicat ing joint deviation (an angle) from neutral posture, within which the perce ived comfort for different body joint postures is expected to be the same. An experiment for quantifying perceived comfort ratings was conducted using the free modulus method of magnitude estimation. Based on experimental res ults, regression equations were derived for each joint posture, to represen t the relationships between different levels of joint deviation/joint postu re and corresponding normalized comfort scores. The JAI values were develop ed for nine verbal categories of joint comfort. The JAIs with the marginal comfort levels, one of the nine verbal categories used, for most joint post ures around the wrist, elbow, neck and ankle were similar to the maximum ra nge of motion (ROM) values for these joints. However, the JAIs with the mar ginal comfort category for back and hip postures were much smaller than the maximum ROM values for these joints. There were no significant differences in JAI expressed in terms of the percentage of the corresponding maximum R OM values between sitting and standing postures. The relative 'marginal com fort index', defined as the percentage of JAIs for the marginal comfort rel ative to the corresponding maximum ROM values, for the hip was the smallest among all joints. This was followed, in an increasing order of the margina l comfort index, by the lower back and shoulder, while the marginal comfort index for the elbow joint was the largest. The results of this study sugge st that static postures maintained for 60 s cause greater discomfort for th e hip joint than for the other joints studied, and less discomfort for the elbow than for the other joints. The data about JAIs can be used as guideli nes for enhancing postural comfort when designing a variety of human-machin e tasks where static postures cannot be eliminated.