Switching running shoes often might spare you an injury. Researchers found that recreational runners who regularly rotated between pairs (most used completely different brands or models) were 39 percent less likely to suffer a running-related injury than those who run in the same shoes every time. Throughout the 22-week study, most of the participants who experienced leg or lower-back pain (87 in 264 participants experienced leg or lower-back pain that sidelined them from running for at least one day) ran in just one kind of shoe.

"Different shoes might induce variations in running style, spreading the load of training volume," says study author Daniel Theisen, head of the Sports Medicine Research Laboratory in Luxembourg. He says rotating also lets you progressively introduce new shoes into your training, rather than having to change abruptly from a worn-in pair to a new one. "Having multiple shoes doesn't even cost more," he says, "because you'll be able to keep each pair longer."