Thoracopelvic Coordination of Pregnant Women During Gait


1McCrory J.L., FASCM, 2Seay J.F., 3Hamill J., FACSM, 1West Virginia University, Morgantown, WV, 2U.S. Army Research Institute of Environmental Medicine, Natick, MA, 3University of Massachusetts, Amherst, MA, USA

Pregnant women experience dramatic alterations to the shape of their bodies, particularly in the torso. These changes contribute to a “waddling” gait later in pregnancy, which has been defined as greater thoracic extension, anterior pelvic tilt, and mediolateral translation of the torso compared to non-pregnant women. These changes could also increase chances of having pregnancy-related back pain, which has been reported by 50% of pregnant women. Other populations with low back pain exhibit changes in the coordination pattern between the thorax (i.e. upper torso) and pelvis during gait. The Purpose of this study was to examine the effect of advancing pregnancy on thoracopelvic coordination during gait. Methods: Data were collected on 29 pregnant participants in their 2nd and 3rd trimesters and on 40 control women. An 8 camera motion capture system (120 Hz) was used to collect 3D angular data of the thorax and pelvis while subjects walked at their freely chosen speed along an 8m laboratory runway. The thorax was modeled with markers placed on the manubrium, xyphoid process, and spinous processes of the C7 and T10 vertebrae. The pelvis was modeled with markers placed bilaterally on the ASIS and PSIS. Coordination between the thorax and pelvis during early stance, midstance, late stance, and swing was calculated via a vector coding technique. A MANOVA was performed to determine if differences existed in the coupling angle between the thorax and pelvis between pregnant women in each trimester and controls (α=0.05). Tukey post-hoc tests were performed when appropriate. Results: The frontal plane coupling angle was greater in late stance during the 3rd trimester (223.3±63.4º) than in the 2nd trimester (198.7±63.4º; p = 0.01) or in controls (198.6±63.2º; p=0.02). No differences were noted in the coupling angles in the sagittal or transverse planes. Conclusion: Pregnant women are said to “waddle.” While previous studies have reported no alterations in the frontal plane angular movement of the thorax and pelvis individually during gait, we found that the frontal plane phase angle is increased in the third trimester, such that the pelvis and trunk had more in-phase coordination in the third trimester compared to controls. This change in coordination mechanics may be related to the high incidence of back pain in pregnant women.

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