Risks involve mechanics, not just chance
By Emily Delzell
Pregnancy changes gait and balance, and in ways that increase the risk of falling in certain women. Research suggests falls aren’t caused by environmental differences and that exercise confers a protective effect, according to investigators from West Virginia University in Morgantown, whose most recent data appeared in the August issue of Gait & Posture.
As part of their ongoing research on biomechanical changes during pregnancy, Jean McCrory, PhD, assistant professor in the WVU Department of Human Performance and Applied Exercise Science, and colleagues evaluated balance measures in women during both their second and third trimesters; 15 fell and 14 did not. Forty nonpregnant women served as controls.
The Gait & Posture paper analyzed participants as they walked at self-selected walking speeds along an 8-m walkway with an embedded force plate. When walking velocity was included as a covariate, investigators found no significant differences in ground reaction forces (GRFs) or center of pressure (COP) between trimesters or fallers and nonfallers.
Other research conducted with the same participants, however, did demonstrate differences in balance measures.
In a 2010 paper in the British Journal of Obstetrics and Gynecology, McCrory tested dynamic postural stability variables by having women stand on a force plate that translated back and forth. Initial sway, total sway, and sway velocity were smaller in fallers than in nonfallers and controls (P<0.05) and there were no differences between controls and nonfallers.
A second 2010 paper published in the Journal of Biomechanics found women in their third trimesters had less initial sway, total sway, and sway velocity than in their second trimesters and compared with controls (P<0.05). McCrory and colleagues found no differences between controls and women in their second trimesters.
In an abstract presented in August at the American Society of Biomechanics meeting in Long Beach, CA, McCrory’s group found that, during stair ascension, mediolateral GRF was greater in pregnant fallers than in nonfallers and controls and that fallers also had a longer time to maximum breaking force and a greater braking impulse.
“I thought falls happened by chance, that is, because of differences in environmental factors, but in the controlled lab environment, we found differences in balance between fallers and nonfallers and in later versus earlier pregnancy,” McCrory said.
When a healthy, nonpregnant individual experiences a backward perturbation, the COP moves forward.
“Pregnant fallers don’t seem to have this same movement. I suspect that the gastroc and the soleus [muscles] aren’t being activated appropriately,” she said, adding, “We also asked women if they exercised or not. Among the pregnant women, seven were sedentary and all these women fell. Exercise may help women adapt to the ongoing changes of pregnancy and recover better from potential falls.”
The differences in GRFs noted in the ASB abstract, however, are not related to reaction time, but to some mechanical difference that makes pregnant women more likely to slip as they climb stairs, McCrory said.
The protective effect of exercise was not surprising to Robert J. Butler, PT, DPT, PhD, an assistant professor of physical therapy at Duke University who has investigated gait changes in women wearing an “empathy belly” that simulates pregnancy.
“Pregnancy means the body is continually adapting to new forces,” he said. “Exercise likely confers better proprioception—nonfallers are more aware of how their body responds and neuromuscular activation pathways are more advanced; you’d expect exercisers to recover faster than sedentary individuals.”
One of the primary messages of such research, said Butler, is that, “Many changes occur during pregnancy and it’s appropriate for a movement practitioner to address these issues and help new mothers normalize movements in the months following birth.”
McCrory noted that future research should address both postpartum gait retraining as well methods that can identify pregnant women at risk for falling.