While carrying less weight may make athletes run faster, it may also put them at a higher risk for injuries, especially in females, a study has claimed.

The new study found that female runners who have a body mass index (BMI) of less than 19 are at a higher risk of developing stress fractures -- a tiny crack in a bone caused by repetitive stress or force, often from overuse -- than women 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."One of the most important factors we identified that put female runners at an increased risk of developing a stress fracture was low body weight, or low body mass index," said Timothy Miller, Assistant Professor from The Ohio State University in the US.

Runners endure repetitive pounding on hard surfaces and, without enough lean muscle mass for dissipation of impact forces, the bones of the legs are vulnerable."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 optimised, runners remain at increased risk of developing a stress fracture," Miller explained, in the paper published in the journal Current Orthopaedic Practice.Further, 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.

Previous studies show that between 25 and 50 percent of track athletes have at least one stress fracture in their career, with an increased incidence in female track athletes."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 noted.