The relationships between lumbar curves, pelvic tilt and joint mobilities in different sitting postures in young adult males.

The lumbar lordosis and pelvic tilt of twenty male subjects were measured in standing and in three different sitting postures with the trunk-thigh angles of 120 (sitting A), 90 (sitting B), and 60 (sitting C) degs and the knee angle was constant at 90 deg. Ten more male subjects participated in the supplemental study, in which additional condition of the knee angle was employed in postures of the trunk-thigh angles of 90 and 60 degs. Some joint mobilities were also measured to investigate the relations of the mobilities to lumbar lordosis and pelvic tilt. The lumbar curve decreased and the pelvis rotated rearward significantly as the trunk-thigh angle and the knee flexion decreased. The great alteration of the lumbar curve was observed between standing and sitting A, which was much different from the results of Keegan (1953) studied in the subjects of lateral recumbent position. There was a high correlation coefficient between the lumbar curve and the pelvic tilt (r = 0.909), so that the relations of the pelvic tilt to the joint mobilities were investigated. When the knee angle was constant, the pelvic tilt is related significantly to the hamstrings between standing and sitting A and to the gluteus maximus between sitting A and sitting C. However, at different sitting postures with the trunk-thigh angles of 90 and 60 degs involving different knee flexions, hamstrings added to gluteal muscles affected significantly lumbar curve and pelvic tilting.(ABSTRACT TRUNCATED AT 250 WORDS)