Final answer:
Pregnant women often suffer from back strain late in their pregnancy due to increased weight distribution and hormonal changes affecting posture.
Step-by-step explanation:
Pregnant women often suffer from back strain late in their pregnancy due to several factors. One of the main reasons is the increased weight distribution caused by the growing fetus and the enlarging uterus. This puts extra pressure on the lower back and can lead to discomfort and strain. Additionally, hormonal changes during pregnancy can affect posture, causing pregnant women to adjust their shoulder position and increase the curvature in their spine, increasing the shear component of stress on the lower vertebrae.