Shoe companies market different sneaker models to runners based on how their feet roll and distribute their weight when they hit the ground -- a term referred to as pronation.

Overpronators have feet that roll too far inward on each stride, while the feet of underpronators don't roll enough. Shoes are marketed under the assumption that by adjusting for some of these differences, runners can improve their mechanics and thus prevent injury.

Pronation is generally measured by taking a flat footprint and examining how much of the foot is in contact with the ground when the runner is standing still, a method used by many running specialty stores. But Marine Corps recruits who were fitted for sneakers this way got injured just as frequently as those who were all given a basic shoe made for runners who pronate normally.

During the study, Knapik and his colleagues kept track of different kinds of injuries in the recruits, including overuse injuries and injuries to tendons and ligaments as well as bones and muscles.

In every way the study team measured injuries, there was little difference in how often members of the two groups got injured. This was true for both men and women.

In all, about 42 percent of men assigned custom fitted shoes and 41 percent of men in the stability shoe group got injured over the 12-week training period. For women, approximately 37 percent in custom fitted shoes and about 45 percent in stability shoes regardless of their foot type were injured -- a difference that was not statistically significant.