Analysis of ground reaction forces in the second and third trimesters of pregnancy during walking

The objective of the current study was to examine the effect of pregnancy during the 2nd and 3rd trimesters on ground reaction forces (GRFs). Twenty-four non-pregnant women and forty-eight pregnant women in the second and third trimesters participated in this cross-sectional study. Qualisys Gait Analysis System was used to analyze peaks and time parameters of GRFs in vertical (Fz), antero-posterior (Fx) and medio-lateral directions (Fy). The results showed that there were no significant differences between the non-pregnant and the pregnant women in the first peak (Fz1) (p=.147) and the second peak (Fz2) (p=.125) of vertical GRF, braking force (FyB) (p=.867) and propulsion force (FyP) (p=.929), as well as lateral (FxL) (p=0.994) and medial (FxM) GRF (p=.920). However, there was a significant increase in the Fz minimum (min) (p=.008), and a decrease in the difference between the Fz1 and Fz min (p=.042) and the difference between Fz2 and Fz min (p=.028). Moreover, there were increases in the time taken to reach the Fz1 (p=.024), Fz2 (p=.005), Fz min (=0.001), FyB (p=.010), FyP (p=.001), FxL (p=.010) and FxM (p=.011). These findings displayed that the pregnant women assumed a flatter pattern of vertical GRF and a decreased downward movement of center of gravity. This pattern may help to make the gait smooth and efficient. Increased time to reach peaks of GRFs may be a strategy to maximize balance during pregnancy.