An increasing number of runners are turning to minimalist running shoes for their alleged performance benefits, but a small study of runners shows that the shoes are more likely to lead to bone injury than conventional ones.

Minimalist shoes aim to mimic the experience of running barefoot and are thought to help promote a more natural running gait and strengthen the muscles in the feet and lower legs.

But “there is little conclusive evidence about the advantages or disadvantages of running in these shoes,” researchers from Brigham Young University wrote in a paper that appeared in the journal Medicine & Science in Sports & Exercise. “While performance benefits may exist, injury may also occur from the added stress of running without the benefit of cushioning under the foot.”

The BYU team decided to look at how Vibram FiveFingers, one of the more popular brands of minimalist running shoes, affected injury rates in a small pool of runners.

Thirty-six experienced recreational runners took part in the study. Seventeen of them ran in traditional running shoes for 10 weeks, while 19 gradually transitioned to Vibram FiveFingers shoes over a 10-week period. None of the participants had a lower-leg injury serious enough to keep them from running at least three times per week in the six-month period leading up to the study. None of the 36 subjects had run in FiveFingers shoes before.

The runners that transitioned to Vibrams adopted a transition plan recommended by the company at the time of the study -- a single run between one and two miles in Vibrams during the first week, two runs in Vibrams the second week and three runs in the minimalist shoes the third. For the rest of the study period, the subjects could increase the amount they ran in the Vibrams as much as they felt comfortable with.

MRIs taken of feet before the experimental period showed no significant differences between the transition group and the control group. But 10 weeks later, MRIs revealed that 10 out of 19 of the runners in the group wearing Vibrams had increases in bone marrow edema -- excess fluid in the bone, which can lead to inflammation. Two of the runners in the Vibrams group suffered foot stress fractures.

In the control group, just one of the 17 runners saw an increase in bone marrow edema.

“It's worth noting that in their peak mileage week during the 10-week study, the conventional-shoe runners reported more average mileage (30) than either the Vibrams runners who didn't get injured (about 18 miles) or the Vibrams runners who got injured (about 15 miles),” Runners World pointed out.

A representative for VibramUSA said the company was declining to comment on the study, due to ongoing litigation. Vibram USA and Vibram Fivefingers LLC have been targeted with punative class-action lawsuits in California and Massachusetts from consumers who say the company’s claims about the shoes’ health benefits are misleading.

Vibram does put warnings on its product and website, urging customers to take a measured, slow approach when transitioning to running in FiveFingers and to watch out for foot pain. The BYU researchers echoed this cautionary approach.

“Runners interested in transitioning to minimalist running shoes, such as Vibram FiveFingers, should transition very slowly and gradually in order to avoid potential stress injury in the foot,” the authors wrote.

SOURCE: Ridge et al. “Foot Bone Marrow Edema after 10-week Transition to Minimalist Running Shoes.” Medicine & Science in Sports & Exercise, published Feb. 22, 2013.