A longitudinal study of the effect of pregnancy on rising to stand from a chair.

Rising to stand from a chair becomes more difficult to perform as pregnancy progresses, which may lead to altered biomechanics affecting the musculoskeletal demands on the body segments. The kinematic and kinetic adaptations in the lower limbs and trunk as pregnancy progresses are unknown. Nine maternal subjects were investigated using an eight-camera motion analysis system and two force plates, four times throughout pregnancy and once post-birth during rising to stand. Twelve nulliparous female subjects were used to establish natural variation with retesting over the time period. The maternal subjects used temporal-spatial, kinematic and kinetic strategies to widen the base of support, minimize propulsion, increase motion of the thoracic segment and minimize anterior trunk-thigh apposition. A fear of postural instability may have made the subjects more cautious, and as they were able to adequately flex the trunk forward, propulsion was minimized in favor of maintaining upright terminal balance.