Effect of posture on hip joint moment during pregnancy, while performing a standing task

In this paper the combined effect on reactive hip joint moment due to changes in (1) segment mass, (2) trunk centre of mass, and (3) working posture during pregnancy was estimated, and the relative contributions of these three changes to the change in the moment were assessed. The situation studied concerned standing work at a table. Sixteen women were studied monthly during pregnancy. The working posture was assessed by two-dimensional photographic posture recording and description. Body dimensions were measured to assess segment characteristics. A two-dimensional static model was used to estimate the reactive hip joint moment at 10, 20, 30 and 40 weeks of pregnancy. Between 10 and 40 weeks of pregnancy the moment increase was 52 Nm, i.e. the load at 40 weeks of pregnancy is 2.8 times the load at 10 weeks of pregnancy. On average half of this increase was due to postural changes. Changes in segment mass, trunk centre of mass, and the interaction between the three changes accounted for rougly 10, 20 and 15% of the load increase respectively. The increase in reactive hip joint moment may be minimized by preventing adverse postural changes, and optimizing the posture to reduce the contribution of changes in body weight (distribution).