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Biomechanical stability of pregnant women.

McCrory-JL; Redfern-MS; Cavanagh-PR; Daftary-A; Mazumdar-S; Schwerha-J
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, K01-OH-008548, 2009 Apr; :1-47
Approximately 27% of pregnant women report a fall during their pregnancies. Pregnant women undergo numerous anatomical, physiological, and hormonal changes that may be related to an increased risk of falling. Factors that contribute to this increase risk of falling are unknown, as little research has been performed to study gait and postural stability biomechanics during pregnancy. The purpose of this research study was to investigate the changes to dynamic stability of pregnant women during gait, stair ascent and descent, and perturbed stance. We hypothesized the following would occur with advancing pregnancy: the anterior position of the center of mass with respect to the base of support, the trial to trial intra-subject variability on selected gait parameters, the required joint torques, and the reaction time and response amplitude in response to a mild postural perturbation would all increase. Methods: Forty one pregnant women (age: 29.S+/-4.9 yrs, hgt: 1.7+/-0.7 m, 2nd trimester mass: 74.7+/-12.1 kg, 3rd trimester mass: 81.6+/-11.0 kg) and 40 non-pregnant controls (age: 26.S+/-6.4 yrs, hgt: 1.7+/-0.6 m, mass: 66.0+/-8.9 kg) participated. Data were collected on the pregnant women in the middle of their 2nd and 3rd trimesters and on the control women in the week following menses. After obtaining consent, pregnant subjects were surveyed about previous pregnancies, current exercise participation, current employment, as well as history of falls while pregnant. Thirty-two anthropometric measures were recorded to determine the location of the center of mass of the torso. Biomechanical movement data were collected of the subject during gait, as well as during stair ascent and descent. Dynamic postural stability data were collected using an Equitest system (NeuroCom Inc., Clackamas, OR). For each of the gait variables, a two-factor ANOVA was performed with group (control or pregnant) and trimester as the independent variables (a=O.OS). For the balance data, a mixed-model ANOVA was performed on each variable (a=O.OS). Additionally, 60% of the pregnant subjects reported falling. Therefore, subsequent two-factor ANOV As were performed on the gait and balance data with group (control, pregnant faller, pregnant non-faller), and trimester as the independent variables (a=O.OS). Results: Pregnant women did not demonstrate greater mediolateral motion at either the COM or at C7 when compared to the control group. The BoS was wider during pregnancy, as expected. The nonpregnant control group exhibited greater knee flexion moments than the pregnant group. The amount of variability of these measures was not increased during pregnancy. For the balance data, reaction time was not different between the pregnant women and controls, regardless of trimester. Initial sway, total sway, and sway velocity were significantly less during the 3'd trimester than during the 2nd trimester and when compared to the non-pregnant controls. No differences were found in any of the measures between the pregnant women in their 2nd trimesters and the control group. When comparing the pregnant fallers, non-fallers, and controls, reaction time was not different between the pregnant fallers, pregnant non-fallers, and nonpregnant controls. Initial sway, sway velocity, and total sway were less in the pregnant fallers when compared to the pregnant non-fallers and controls. No differences were noted between the latter two groups. Thirty-one pregnant subjects reported exercise participation. Sedentary women were more likely to fall than active women. Pregnant workers were not more likely to fall than pregnant women who were not employed. Applications for NIOSH: In the workplace, both employers and employees should be aware that dynamic balance in reaction to a perturbation, such as a trip or a slip, may be significantly impaired in the third trimester of pregnancy. Exercise participation may help to reduce the incidence of falls.
Humans; Women; Pregnancy; Posture; Risk-factors; Age-groups; Physical-capacity; Physical-fitness; Physiological-factors; Physiological-function; Physiology; Biomechanics
Jean L. McCrory PhD, West Virginia University, Department of Human Performance and Applied Exercise Science, Division of Exercise Physiology, 8315 RCB Health Sciences Center, South, PO Box 9227, Morgantown, WV 26506-9227
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National Institute for Occupational Safety and Health
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University of Pittsburgh