The shoe market has recently been glutted with a new wave of "toner" sneakers promising a better body simply by walking. At first blush, these new kicks seem like the most magical footwear since Dorothy's ruby slippers. But consumers are right to ask whether the shoes are based on sound science or marketing gimmickry. With price tags ranging from $100 to $245, are they designed to firm up bottoms or bottom lines?
These shoes—MBTs, Skechers Shape-ups, and Reebok EasyTones, for example—eschew stability for instability, incorporating thicker, curvier soles, which are intended to activate muscles people don't normally use. "Tone your legs and butt with every step," boasts the EasyTone Web site. "Make your bottom half your better half," crows Skechers. Better posture! Harder abs! Firmer butts! Just look at the women in our videos!
The MBT and the Shape-up both incorporate a "rocker-bottom sole," developed by MBT several years ago. The base of the shoe resembles the bottom of a rocking chair, a thick, curved platform that rolls from heel to toe with each step, stabilizing the foot muscles while destabilizing the gait. Reebok's EasyTone subscribes to the "instability is good" philosophy by equipping the sole with two thick pads, one on the ball and one on the heel of the shoe.
Recently, researchers from the American Council on Exercise decided to put the toners to the test. They recruited subjects; laced them up in EasyTones, Shape-ups, and MBTs; and put them on treadmills. Then they used electromyography to measure the muscle activation in their calves, quads, hamstrings, buttocks, back, and abs. The researchers found no significant increase in muscle activity when comparing toners to normal sneakers.
"There is simply no evidence to support the claims that these shoes will help wearers exercise more intensely, burn more calories, or improve muscle strength and tone," the report found. But some doctors have noted that the rocker soles do have therapeutic benefits for people with specific conditions. "They can reduce strain on certain joints, which benefits people with arthritis, and they're good for people with soreness and calluses on their feet," says Connecticut podiatrist Josh White, who works with diabetes patients. Some doctors prescribe them to arthritic patients as substitutes for air casts.
Rocker soles are only part of a broader attempt by shoe companies to convince consumers that they are naturally designed to walk barefoot. According to manufacturers, humans crave uneven surfaces like beaches and marshes, and long to return to their natural peripatetic roots. Ironically, shoe marketers now say that over their 9,000-year history, shoes have mucked up our natural gaits, leading to poor posture, weak joints, and bad backs. MBTs, in fact, are marketed as "the anti-shoe." But shoes like Vibram's FiveFingers take that trend further: the FiveFinger is little more than a thin, flexible sheath contoured to the shape of the foot, giving it full range of motion. Rather than adding excess cushioning to the sole, the manufacturers carve much of it away, which places emphasis on the foot muscles and receptors, and provides stability as opposed to instability. The shoes look like flippers without fins, and consumers are encouraged to work out in them.
There is debate about whether this all makes sense. "Most scientists agree that humans should never have put a sneaker on their foot," says Jeff Staple, a New York-based designer and curator who works for sneaker-shoe companies including Nike, New Balance, and Airwalk, and an owner of more than 500 pairs of shoes. "Our caveman brothers and sisters never had scoliosis." He enjoys the way the FiveFingers brings his feet closer to the ground and also favors the Nike Free, which employs a similar concept.
"They're the new rage in running," says David Levine, a Maryland podiatrist. But like other doctors, he's skeptical because people's muscles haven't been conditioned to run with so little protection. "It sets you up for injury," he says. He concedes that the shoe might be good for a small minority of people with excellent feet who like the nuanced sensation of the ground and don't mind taking a short-term pounding. "Eventually, the benefit will wear out," he says, and people will develop foot problems.
Connecticut podiatrist White, who appreciates the appeal of walking barefoot, nevertheless has another concern. "The FiveFingers might be the best in terms of physics, but some people wouldn't be caught dead in them because they look so odd," he says. Ultimately, he says, it's a good shoe if used on soft surfaces.
Shock-absorbing shoes are almost the opposite of barefoot technology: they add extra padding and support. For instance, Nike Shox incorporates spring-like material beneath the heel of the foot, which absorbs shock from impact and purportedly generates lift. The design raises the question: how much shock absorption is healthy, and how much is too much? Several other shoe innovations have attempted to solve this question, from Nike Air to Asics Gel and New Balance Abzorb.
Podiatrist Levine says that Shox can present problems for some people. Because the backs of the soles are so cushy, he says, the heels could be injured if they strike the ground too hard. White worries about lateral support. "The tradeoff to cushioning is side-to-side instability," he says.
David Barton--owner of David Barton Gym, which has locations in New York, Miami, Chicago, and Seattle--acknowledges that the elevated heel is great for people with bad joints or plantar fasciitis. "On the downside," he says, "the Shox can reduce lateral stability, shorten your calf, cause calf tightness, and diminish hamstring and glute-muscle recruitment."
Barton says he favors shoes that promote a feeling of barefoot walking, like the FiveFingers. "The human body suffered a evolutionary blow when the shoe was invented," he says. "It was a huge score for fashion but a step in the wrong direction for biological efficiency."
These flip-flops are essentially an open-toed incarnation of toner technology, promising to tighten your leg muscles and alleviate hip, knee, and back pain by eliciting a rolling motion and creating instability that requires the muscles to compensate. The product was designed by two biomechanics specialists from the Human Performance Center at London's South Bank University. The product's Web site contains a heap of hard-to-understand scientific language— it boasts that they're built with a "patent-pending, muscle-loading Microwobbleboard technology"—along with a video featuring an electromyography treadmill test of its own. Since unveiling their flip-flop design, the makers have released other shoes and boots based on similar technology.
Podiatrists actually give FitFlops a thumbs-up, but not for the reasons the shoemakers would have you believe. The reason these shoes are good, say doctors, is because an increasing number of patients visit their offices with foot injuries caused by flip-flops. At least with FitFlops, they say, the extra padding can absorb some of the shock that comes along with extended use. "It's a vast improvement over wearing regular sandals," says Jay Levine (no relation to David), a shoe designer and the director of podiatric surgery at Good Samaritan Hospital, in Suffern, N.Y.
Dr. Scholl's Custom Fit Orthotic Inserts are stocked in hundreds of drugstores across the country and promise better arch support at cheaper prices. Customers are instructed to remove their shoes and step on the platform of a kiosk, where 2,000 pressure sensors purportedly read and analyze the shape of their feet. Moments later, a message is sent to a monitor, where the customer sees an image of his or her feet and receives a recommendation on which insert to purchase.
Experts are split on the inserts' benefits, though most point to small positive characteristics that don't outweigh custom-made orthotics. "They've come up with a pretty good product for the entry-level orthotic," says Jay Levine. "If someone doesn't have a lot of money, I think it could work, as much as saying that might hurt my business." David Levine, however, warns that the term "orthotic" shouldn't be used too freely. "They should be called arch supports," he says. "An orthotic is custom-made, molded to the foot, not something that's mass-produced." If someone has flat feet, store-bought arch supports will just feel like lumps, because only a true orthotic can completely hold a foot in its proper position, he says.