TODD BYERS was among more than 20,000 people running the San Francisco Marathon last month. Dressed in shorts and a T-shirt, he might have blended in with the other runners, except for one glaring difference: he was barefoot.

Even in anything-goes San Francisco, his lack of footwear prompted curious stares. His photo was snapped, and he heard one runner grumble, “I just don’t want the guy without shoes to beat me.”

Mr. Byers, 46, a running coach and event manager from Long Beach, Calif., who clocked in at 4 hours 48 minutes, has run 75 marathons since 2004 in bare feet. “People are kind of weird about it,” he shrugs.

Maybe they shouldn’t be. Recent research suggests that for all their high-tech features, modern running shoes may not actually do much to improve a runner’s performance or prevent injuries. Some runners are convinced that they are better off with shoes that are little more than thin gloves for the feet  or with no shoes at all.