More fleet. A 2012 study found that experienced runners were more efficient (meaning they used less oxygen) in barefoot shoes than other footwear. In the real world, that could translate to greater speed.
Less wobble. People wearing Vibram FiveFingers (pictured) are better able to estimate a treadmill's slope than those wearing cushiony shoes, according a 2011 study. They had improved "proprioception"—the sense of how one's body is positioned in space—which can lead to steadier balance.
Sore calves. Aching arches. Fractured foot bones. The body moves differently in minimalist shoes, experts say. Muscles and tendons, unused to new stresses, may give way if you do too much too soon. Chat boards teem with reports of barefoot-shoe-related afflictions. Although little reliable research exists yet, it's clear that these shoes are no guarantee against injury. The American Council of Exercise advises allowing yourself time to adapt. If you buy a pair, wear them only a few minutes a day at first.
Smelly feet. Unless you invest in toe socks (available at some specialty running stores), the shoes will soon reek. You can wash them, but even so, the bouquet lingers.
Separated toes. There doesn't seem to be any scientific evidence showing that encased toes improve performance or comfort. They do, however, make donning the shoes arduous.
Next: Should you go barefoot?