A quantitative investigation of lumbar and pelvic postures in standing and sitting: Interrelationships with body position and hip muscle length

Abstract

Lumbar angles, pelvic tilts and hip muscle indices of 25 female and 25 male subjects were measured in standing and in a variety of body positions in order to test hypotheses derived from the model of standing and sitting posture expounded by authors such as Keegan (1953) and later by Mandal (1991). The model emphasises the interrelationship between the anterior and posterior thigh muscles and tilt of the pelvis in determining spinal posture in different body positions. The posterior trunk-thigh muscles are held to play a major role in the flattening of the lumbar spine in sitting and the anterior trunk-thigh muscles in accentuating the lumbar curve in standing. A quantitative test of hypotheses derived from the model carried out. Spinal angles and pelvic tilts were measured using an inclinometer. An angular index of iliopsoas muscle length proved the best predictor of postural adaptation. A supplementary investigation clarified the role of the hamstrings in postural adaptation. The findings support and extend those of other recent researchers but draw attention to the effects of body position of lumbo-pelvic constraint as well as the mechanisms of loss of lumbar lordosis in sitting. Some potential problems of postural stress in standing - caused by excessive lumbar lordosis - are suggested as well as implications for research into working posture in developing countries.