Abstract
The purpose of this study was to show the effect of change in posture and movement during pregnancy on the lower back using a three-dimensional motion analysis system. Three pregnant women participated in this study when they were in the sixth and eighth months of pregnancy. Trunk forward and backward moments during static standing and level walking were analyzed. The trunk forward and backward moments were in proportion to trunk bending angle in two subjects. However, the trunk forward and backward moments decreased in spite of the increase in trunk bending angle with pregnancy progress in one subject. These results suggest that center of gravity of HAT (head, arm, trunk) moved anteroinferior due to abdominal swelling in pregnancy resulting in shorter lever arm between joint centre and gravitational force. The trunk backward moment decreased in the second half of a double stance phase in walking because inertial force applied to centre of gravity in HAT and trunk angle affected trunk moment. However, one subject did not exert trunk backward moment in spite of increased trunk forward bending angle and backward component of floor reaction force. This was also due to center of gravity of HAT moving anteroinferior resulting in shorter lever arm.
