Ground reaction forces during stair locomotion in pregnancy

Pregnant women experience numerous physical alterations during pregnancy which may place them at an increased risk of falls. The purpose of this study was to examine ground reaction forces (GRFs) during staircase locomotion in pregnant and non-pregnant women. Methods Data were collected on 29 pregnant women in their second and third trimesters, and on 40 control women. Subjects walked at their freely chosen speeds during stair ascent and descent. A force plate imbedded in the second stair, but structurally independent of the staircase, was used to collect GRF data (1080 Hz). A marker placed on the L3/L4 spinal segment was used to determine ascent and descent velocity from a motion-capture system. In the statistical analyses, trimester (control, second trimester, third trimester) and subject were the independent variables. Stance time and ascent/descent velocity were analyzed with an ANOVA. Mediolateral excursion of the COP during the step was analyzed with an ANCOVA. The GRFs were categorized into anterioposterior, mediolateral, and vertical forces. A two factor MANCOVA (subject, trimester) was performed on each GRF category. Mass and velocity served as covariates in each analysis (α = 0.05). Results The mediolateral excursion of the COP during ascent was greater in the third trimester (p = 0.04). The anterioposterior braking impulse was greater in both ascent (p = 0.01) and descent (p = 0.01) during pregnancy. The vertical GRF loading rate during descent was greater in pregnant women than in controls (p = 0.04). Conclusion These alterations are likely related to increased instability during stairway walking and could contribute to increased fall risk during pregnancy.