Sit-to-stand at different periods of pregnancy

Objective. This study was performed to determine the biomechanics of chair rising by pregnant women. Design. Relative body joint position and ground reaction forces were measur ed by a motion analysis system and one force plate. Background. Physiological and psychological changes during pregnancy impose postural demands and limit the performance of daily living activities such as rising from sitting to standing position. Methods. Twenty-four pregnant women, divided into three groups, were studie d performing sit-to-stand transition from an armless and adjustable chair. By kinematic and kinetic analysis, the angles and moments of hip, knee and ankle joints were investigated. Results. The chair height has great influence on knee joint and hip joint m oments, but less on ankle joints. In the third trimester for all chair heig hts, because of a marked increase in abdominal depth, the maximum hip momen t is significantly less than that in first trimester, while the maximum kne e moment is significantly larger. Pregnant women in third trimester produce d larger knee moment during sit-to-stand transition from lower chair height . Conclusion. The mechanism of sit-to-stand is affected by the physical chang es of pregnant women at different periods of pregnancy, e.g. increased load ing of knee joint and decreased hip joint moment, especially in the last tr imester period of pregnancy.