If you’re thinking of trying out those ‘barefoot’ running shoes, take it slow—or your risk of stress injuries and fractures increases. A Brigham Young University study published in Medicine & Science in Sports & Exercise found that runners who transition too quickly to minimalist shoes experienced greater rates on injury to their foot bones, including stress fractures.

In the study, researchers gave runners a baseline MRI scan and had them follow a minimalist shoe industry-suggested protocol. Participants performed one 1-2 mile run in the minimalist shoes the first week, and added an additional short run each week so that they ran at least 3 miles in the new shoes by week three. They were then told to add miles as they felt comfortable.

After 10 weeks, runners were again given MRI scans—which revealed that those who had transitioned to the minimalist shoes had greater bone marrow edemas and more stress injuries than those in traditional shoes. The results of this study suggest that runners take it slow when transitioning to dramatically new running shoes.