Women who walk with flat feet are 50 percent more likely than those with normal or high arches to have low back pain, a new study suggests.
"The key takeaway from the study is that if women have low back pain, it may not be just the back," said senior author Marian Hannan of the Institute for Aging Research at Hebrew SeniorLife in Boston.
"It turns out that feet are important for the back."
Past research has hinted that low back pain, which affects roughly one in five people worldwide, could be related to the shape of the foot's arch in the standing position.
Among 1,930 men and women recruited from Framingham, Massachusetts, pronated feet - which tend to roll inward as a person walks - were linked to lower back pain in women only.
"There has been only weak correlation between pronated feet and low back pain so I was happy to see some evidence of this in the study," said Christopher Kevin Wong.
He is an associate professor of rehabilitation and regenerative medicine at Columbia University in New York City and was not involved with the current study.
For their study, Hannan and her colleagues measured each person's arch in the standing position. Then participants walked across a mat with embedded sensors to measure pressure from the heel to the tip of the foot while walking.
"It's a method that shows promise, and will need to be validated against other measures of motion analysis," Wong told Reuters Health.
For example, another method includes marking a person's leg with ink at the joints in order to detect under- or over-pronation movements.
Women in the study were in their 60s, on average. About 38 percent overall reported having low back pain.
Dr. Stephen Pinney, an orthopedic surgeon at St. Mary's Medical Center in San Francisco, called the size of the study "impressive."
He told Reuters Health future studies should follow participants with different arches forward in time to confirm these findings. Research should also determine what effect, if any, interventions such as orthotics might have on who develops back pain.
"We've known that putting a patient in a foot cast after surgery, for example, can lead to lower back pain because this creates asymmetric forces on the back," said Pinney, who didn't participate in the new research.
Hannan said the body may use other muscles to help make up for flat feet when a person walks, which could explain the link to back pain.
Standing and walking use the foot in different ways. Both a flat foot in standing position and a pronated foot walking could be something to consider during a doctor's visit, Hannan said.
She and her team suggested reasons why women could be more affected by flat feet while walking than men.
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For example, women's pelvic bones are wider and not as flexible as men's. In general, women rotate their hips more than men while walking. Women also move their upper bodies more than men when they walk.
"Women probably don't know if their foot function contributes to low back pain, but they can find out about it," Hannan said.
She suggested people with low back pain visit a doctor or physical therapist.
One simple trick to strengthen muscles in the feet is to lay a towel on a flat surface and then scrunch the toes together in order to pick up the towel and lower it back down. Foot orthotics are another option.
"Once you have back pain, you'll want to do core muscle exercises and perhaps take anti-inflammatory medication, but anything that is contributing to asymmetry - you will also want to address that," Pinney said.
"There are a bunch of different reasons for getting low back pain, and this adds another category for people to consider," he said.
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