Every woman who experiences pregnancy will experience changes in her body. Some changes will be temporary but others may last forever. Recent studies on the biomechanical changes of pregnancy on female runners shed light on how pregnancy affects their running stride. Most women do not run routinely or for long distances during pregnancy but the way these women are affected by their pregnancies may also affect the walking strides of many, if not most, pregnant women.

The study of pregnant women runners is small, thanks in part to so few women who run avidly during pregnancy. Since stride is important for injury- and pain-free running, these women are ideal study subjects to shed light on how pregnancy affects the stride of less-active women, too.

As pregnancy advances, weight is gained. This added weight shifts a woman’s center of gravity. Her connective tissues loosen up to accommodate the growing abdomen and impending childbirth. These changes cause the walking stride to grow wider and steps shorter. The stride continues to grow shorter and wider as pregnancy progresses until a woman begins to waddle a bit.

The pelvis tilts forward throughout the pregnancy. In the women runners under study, this tilting changed how the runner’s foot landed with each stride. This altered landing is probably more exaggerated in runners than in less active pregnant women but others may experience the same effect.

The runners also experienced side-to-side pelvic movement during a run six months after giving birth. This motion was greater six months after delivery than at the six-month pregnancy mark. One runner experienced this instability of the pelvis a year after giving birth. It caused one foot to hit the ground with greater force than the other, causing considerable pain.

Bryan Heiderscheit, a Professor of Orthopedics and Rehabilitation and Director of the running clinic at the University of Wisconsin in Madison, says the way pregnancy stretches abdominal muscle and connective tissue allows the pelvis to become slightly unmoored and prone to tilting and swaying. He recommends abdominal strengthening exercises to regain strength and correct abnormalities in the walking and running stride after pregnancy.

Heiderscheit says crunches won’t get the job done because they don’t address the deep, small muscles of the abdomen. He recommends pulling the belly in and up several times a day, as if trying to stop the flow of urine. More traditional abdomen-strengthening exercises, such as bridges, planks, and squats, will help, too.

Source: Heiderscheit, BC, et al. “Low back and hip pain in a postpartum runner: applying ultrasound imaging and running analysis.” Journal of Orthopaedic & Sports Physical Therapy. US National Library of Medicine National Institutes of Health. Mar 23, 2012, Web. Dec 3, 2013.