The wrong sock can spoil your marathon attempt, suggest experts examining the effects of ill-fitting footwear on running injuries.

(Relaxnews) – For this Sunday’s Chicago Marathon, Loyola University Medical Center researchers are conducting a first-of-its kind study of race participants to determine if there is a link between foot injuries and ill-fitting running shoes and socks.

Researchers will survey runners seeking treatment for foot and ankle injuries in the podiatry tent, taking measurements of their feet and shoes sizes. The researchers will record how many marathons each runner has completed, the brand and style of the runner’s shoes and socks, as well as an estimation as to how many kilometers each runner has put on their shoes. (Experts recommend replacing your shoes after about 500 miles/805 kilometers.) Runners who use minimalist shoes will not be included in the study.

For eight years, Loyola podiatrist and lead researcher Katherine Dux has volunteered her time in the podiatry tent to treat runners, except in 2010 when she ran the marathon herself. Since many of the injuries she has seen over the years — about 200 to 400 per marathon — are ones she attributes to improper shoes or socks, she decided to investigate further for this year’s race.

When it comes to getting the proper fit for your running shoes, it can be difficult to find the sweet spot, with many runners buying shoes as much as a full size too large to allow for foot swelling during running. Dux advises that when buying running shoes you wear your normal running socks and orthotics, and shop late in the day after your feet have become swollen from walking around. 

Runner’s World magazine advises not to try anything new on marathon day. “Race day is not the time for new shoes, new food or drinks, new clothing, or anything else you haven’t done on several training runs,” the publication writes.