Low BMI in female runners linked to injury risk and stress fractures according to study

When chasing PBs, the traditional approach is the same for men and women; train well and aim to get down to ‘race weight’.  However, a three year long study has revealed that though less weight may make female runners faster, it may also put them at a higher risk for injuries.

Published by Ohio State University, the results indicated that female runners with a BMI of less than 19 are at a higher risk of developing stress fractures than those with a BMI of 19 or higher. It also found that lighter women who suffered stress fractures took longer to recover from them than other runners. Yes, the BMI scale is often a confusing one, but it also offers an easily applied scale in which to explain the findings.

Related: why it's time to say goodbye to BMI

Headed up by Dr. Timothy Miller, assistant professor of clinical orthopaedic surgery and sports medicine, the study noted that runners endure repetitive pounding on hard surfaces and, but most importantly, without enough lean muscle mass for dissipation of impact forces, the bones of the legs are vulnerable.

“One of the most important factors we identified was low body weight, or low body mass index. When body mass index is very low and muscle mass is depleted, there is nowhere for the shock of running to be absorbed other than directly into the bones. Until some muscle mass is developed and BMI is optimized, runners remain at increased risk of developing a stress fracture,” Miller said.

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For three years, Miller and his team looked at injuries in dozens of Division I college athletes using the Kaeding-Miller classification system, a unique system that characterises injuries on a scale of 1 to 5, taking into consideration not only the patient’s symptoms, but also x-ray results, bone scan and computed tomography (CT) images, and magnetic resonance imaging (MRI) findings.

Among those with grade 5 stress fractures - the most severe – the research team found that women whose BMI was 19 or higher took about 13 weeks to recover. Those with a low BMI (below 19), took more than 17 weeks to recover and return to running – a full month longer.

“It’s imperative that women know their BMI and work to maintain a healthy level. They should also include resistance training in their training regimen to strengthen the lower leg to prevent injury, even if that means adding weight from additional muscle mass,” Miller said.

Related: 8 resistance training moves for a stronger body

According to the Centers for Disease Control and Prevention, the body mass index for an average woman is 26. Miller suggests female athletes maintain a body mass index of 20-24.