Can you wobble your way to buns of steel?
The popularity of "toning" shoes, whose unstable soles require you to work muscles harder to stay balanced, suggests consumers are banking on it.
Sales of toning shoes, which cost from $70 to upwards of $200 and have enlisted celebrities like Kim Kardashian and Wayne Gretzky to tout their fitness benefits, soared to $736 million in 2010 from $145 million the year before thanks to the entry of more than a dozen brands into the market, according to market research firm NPD Group.
The ads for many of the shoes, showcasing women with enviably sculpted legs (there are toning shoes for men but the customer base is overwhelmingly female), say that wearing them will help you burn more calories, tone muscles and improve posture. Most manufacturers compare the experience of wearing their shoes to walking on sand.
Foot doctors for years have been prescribing shoes with unstable soles to help patients with foot or ankle arthritis, but can they also get you a few steps closer to firmer thighs?
A closer look
Peer-reviewed studies on shoes made by Masai Barefoot Technology, pioneers of the rocker-bottom shoes that are beveled at the heel and toe, have found that standing and walking in unstable shoes can strengthen neglected foot muscles and provide some knee and low back pain relief, along with other therapeutic benefits. Studies on FitFlops, which use Microwobbleboard technology in the midsole, have found they reduce foot pressure by an average of 25 percent and can absorb 22 percent more shock in the lower legs.
Whether that translates to a better backside is sketchy.
Skechers, whose Shape-ups have a rocker sole and an "ultra-soft Resamax kinetic wedge" for a squishier cushion, points to a study published last year in the journal Clinical Biomechanics that found that people who walked in MBTs burned more calories than while walking barefoot or in normal walking shoes. Previous news stories have cited studies funded by Skechers that found people lost more weight and body fat wearing Shape-ups than flat shoes, but those studies were criticized as being poorly controlled (Skechers declined to provide the studies).
Reebok, whose EasyTones use balance-ball-inspired pods and "Moving Air Technology" to create instability, commissioned a study that found electrical activity was 28 percent greater in buttocks muscles and 11 percent greater in calf muscles for wearers of EasyTones versus a regular Reebok walking shoe.
Neither company provides guidelines for how long or frequently people should wear the shoes to see benefits. They say the shoes are not meant to replace the gym, but rather help people "get more out of every step," said Leonard Armato, president of Skechers Fitness Group.
In search of an independent assessment, the American Council on Exercise last year sponsored a study that found that walking in Sketchers Shape-ups, Reebok EasyTone Reenspire or MBTs was no more effective at burning calories or working muscles than walking in a regular New Balance running shoe. The researchers, from the Exercise and Health Program at the University of Wisconsin at La Crosse, tested muscle activity in the calves, quadriceps, hamstrings, gluteus, abdominals and lower back.
Even if muscles do work harder at first to overcome the instability, the effect dissipates as muscles adjust, said Cedric Bryant, chief science officer for the American Council on Exercise.
But there could be an indirect benefit if toning shoes are encouraging people to walk more, Bryant said. Almost all of the test subjects in the ACE study told the researchers that the toning shoes were more comfortable than traditional running shoes, he said.
In fighting form
Toning shoe companies can cite thousands of testimonials from happy customers, but not everyone's satisfied.
Several lawsuits claiming misleading advertising have been filed against toning shoe manufacturers from Reebok to New Balance, and last summer Skechers was named in a federal class action lawsuit alleging Shape-ups offer no health benefit beyond what regular sneakers provide and can cause injury. This February, an Ohio woman filed a lawsuit claiming that wearing Skechers Shape-ups led her to develop hip fractures.
In a review of injury reports on SaferProducts.gov, a site run by the U.S. Consumer Product Safety Commission, Consumer Reports identified 36 complaints between March and May associated with toning shoes. Most of the reported injuries were minor, including tendinitis and foot, leg, and hip pain, but 15 involved broken bones from falls, some requiring surgery.
No studies have suggested that toning shoes are dangerous or cause pain, according to an article this summer put out by the American Orthopaedic Society for Sports Medicine.
Manufacturers say their shoes are safe if used properly.
"Just as the millions of pairs of high-heel shoes that are sold annually aren't suitable for everyone, Shape-ups may not be either," said Skechers' Armato. Shape-ups come with instructions and users are advised to limit wearing them to 25 to 45 minutes per day for the first two weeks, increasing usage time in 5- to 10-minute increments thereafter only if they're comfortable doing so. They should not be used for running.
Podiatrist Paul Langer of Twin Cities Orthopedics in Minneapolis said that although muscles likely do work harder to overcome the instability of the shoes, he is skeptical that it's to the extent that it will actually burn fat and boost muscle tone.
What they can do, Langer said, is redistribute the pressure on your foot, alleviating stress and strain on the joints, which is helpful for people suffering from arthritis in the foot. People should treat the shoes like fitness tools, Langer said. The most problems he sees are from overuse.
If you're in the market
Podiatrist Paul Langer offered these tips if you plan to buy toning shoes:
•Don't wear them if you have poor balance.
•Try on different kinds to assess which are most comfortable and suitable to your needs.
•Avoid cheap knock-offs, which tend to be flimsy on the sides.
•The shoes can be heavy, some weighing more than 16 ounces per shoe. Take that into account when buying, as heavier shoes can cause more muscle soreness.