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A few years ago, the military began analyzing the shapes of recruits’ feet. Injuries during basic training were rampant, and military authorities hoped that by fitting soldiers with running shoes designed for their foot types, injury rates would drop. Trainees obediently began clambering onto a high-tech light table with a mirror beneath it, designed to help outline a subject’s foot. Evaluators classified the recruits as having high, normal or low arches, and they passed out running shoes accordingly.

Many of us have had a similar experience. For decades, coaches and shoe salesmen have visually assessed runners’ foot types to recommend footwear. Runners with high arches have been directed toward soft, well-cushioned shoes, since it’s thought that high arches prevent adequate pronation, or the inward motion of your foot and ankle as you run. Pronation dissipates some of the forces generated by each stride. Flat-footed, low-arched runners, who tend to over-pronate, have typically been told to try sturdy “motion control” shoes with firm midsoles and Teutonic support features, while runners with normal arches are offered neutral shoes (often called “stability” shoes by the companies that make and categorize them).

But as the military prepared to invest large sums in more arch-diagnosing light tables, someone thought to ask if the practice of assigning running shoes by foot shape actually worked. The approach was entrenched in the sports world and widely accepted. But did it actually reduce injuries? Military researchers checked the scientific literature and found that no studies had been completed that answered that question, so eventually they decided they would have to mount their own. They began fitting thousands of recruits in the Army, Air Force and Marine Corps with either the “right” shoes for their feet or stability shoes.

Over the course of three large studies, the most recent of which was published last month in The American Journal of Sports Medicine, the researchers found almost no correlation at all between wearing the proper running shoes and avoiding injury. Injury rates were high among all the runners, but they were highest among the soldiers who had received shoes designed specifically for their foot types. If anything, wearing the “right” shoes for their particular foot shape had increased trainees’ chances of being hurt.

Scientific rumblings about whether running shoes deliver on their promises have been growing louder in recent years. In 2008, an influential review article in The British Journal of Sports Medicine concluded that sports-medicine specialists should stop recommending running shoes based on a person’s foot posture. No scientific evidence supported the practice, the authors pointed out, concluding that “the true effects” of today’s running shoes “on the health and performance of distance runners remain unknown.”

More recently, a study published online in late June in The British Journal of Sports Medicine produced results similar to those in the military experiments, this time using experienced distance runners as subjects. For the study, 81 women were classified according to their foot postures, a more comprehensive measure of foot type than arch shape. About half of the runners received shoes designated by the shoe companies as appropriate for their particular foot stance (underpronators were given cushiony shoes, overpronators motion-control shoes and so on). The rest received shoes at random. All of the women started a 13-week, half-marathon training program. By the end, about a third had missed training days because of pain, with a majority of the hurt runners wearing shoes specifically designed for their foot postures. (It’s worth noting that across the board, motion-control shoes were the most injurious for the runners. Many overpronators, who, in theory, should have benefited from motion-control shoes, complained of pain and missed training days after wearing them, as did a number of the runners with normal feet and every single underpronating runner assigned to the motion-control shoes.)

The lesson of the newest studies is obvious if perhaps disconcerting to those of us planning to invest in new running shoes this summer. “You can’t simply look at foot type as a basis for buying a running shoe,” says Dr. Bruce H. Jones, the manager of the Injury Prevention Program for the United States Army’s Public Health Command and senior author of the military studies. The widespread belief that flat-footed, overpronating runners need motion-control shoes and that high-arched, underpronating runners will benefit from well-cushioned pairs is quite simply, he adds, “a myth.”

The mythology grew and persists, however, in large part because “in certain aspects, the shoes do work,” says Michael Ryan, Ph.D., the lead author of the study of female half-marathoners and currently a postdoctoral fellow in the department of orthopedics and rehabilitation at the University of Wisconsin, Madison. Motion-control shoes, for instance, do control motion, he says. Biomechanical studies of runners on treadmills repeatedly have proved that pronation is significantly reduced in runners who wear motion-control shoes.

The problem is that “no one knows whether pronation is really the underlying issue,” Dr. Jones says. Few scientific studies have examined how or even if over- or underpronation contributes to running injuries. “There is so much that we still don’t understand about the biomechanics of the lower extremities,” Dr. Jones concludes.

For now, if you’re heading out to buy new running shoes, plan to be your own best advocate. “If a salesperson says you need robust motion-control shoes, ask to try on a few pairs of neutral or stability shoes, too,” Mr. Ryan says. “Go outside and run around the block” in each pair. “If you feel any pain or discomfort, that’s your first veto.” Hand back those shoes. Try several more pairs. “There really are only a few pairs that will fit and feel right” for any individual runner, he says. “My best advice is, turn on your sensors and listen to your body, not to what the salespeople might tell you.”