Changes in balance strategy in the third trimester

[Purpose] The purpose of this study was to elucidate changes in balance strategy during pregnancy from a kinematics perspective. [Subjects] Eight pregnant women and eight non-pregnant women participated. [Methods] A 3D motion analysis system, two force plates, and 10 infrared cameras were used to measure the kinematics of the balance strategy. The 3D motion analysis system was used to analyze performance of the functional reach test (FRT). Parameters were compared between non-pregnant women and pregnant women during each trimester, and between pregnant women in the second and third trimesters. [Results] The FRT of pregnant women was shorter than that of non-pregnant women. Bilateral hip joint extension moments were smaller in pregnant women in the second and third trimesters compared to non-pregnant women. Bilateral ankle plantar flexion moments were larger in pregnant women in their third trimester compared to non-pregnant women. In pregnant women, the right ankle plantar flexion moment was larger in the third trimester than in the second trimester. [Conclusion] These results suggest that forward reach distance is reduced, and that the ankle joint strategy takes precedence over the hip joint strategy in maintaining balance during pregnancy compared to non-pregnancy.