Stability used to be a good thing in a shoe. But the current "fitness" footwear craze takes the opposite approach: By subtly throwing your body off balance, these shoes supposedly help you lose weight and sculpt muscles.
The secret is the shoe's unstable sole. To keep your footing, your body supposedly recruits and strengthens smaller, little-used muscles around the ankle joint. Shoe companies say the increase in muscle activity can lead to more calories burned, improved posture and toned leg muscles.
Yet unstable or rocker-bottom shoes have been used for years as therapeutic footwear, and there's little evidence they provide benefits that the manufacturers claim, said Swedish researcher Nerrolyn Ramstrand, who has studied whether instability shoes can improve balance.
Experts emphasize that it's the squats and lunges — not the shoes — that will revolutionize America's glutes; the health claims amount to hype and clever marketing. Toning, for example, has no standard definition so it can't be measured, said Benno Nigg, director of the University of Calgary's Human Performance Laboratory, which has performed paid studies for shoe companies.
Moreover, shoes with an unstable base might be inappropriate for those who have poor balance to begin with, said Ramstrand. Because of the instability, wearers are discouraged from running or jumping in some of the brands.
Still, some published studies show that unstable shoes do change your body's kinetic patterns and can help reduce knee pain from osteoarthritis. Unstable MBT sandals can reduce moderate lower back pain in golfers, according to one of Nigg's studies, published last year in the Clinical Journal of Sports Medicine.
Shoes "used to just be for protection and fashion," said Nigg, who wears MBTs to help improve his skiing. "Now they're training devices that do something to the body's system."
When I tested five pairs of instability shoes — two pairs of walking shoes, one pair of running shoes and two pairs of sandals — I found they all did one thing: increased mindfulness. Walking felt different, and the shoes made me want to do more of it.
Although some brands can be pricey and most claims are inflated, any shoe that inspires more exercise is worth a try. Here's a closer look at each shoe we tried:
MBT Fora Silver ($245, www.mbt.com)
About the shoe: Dramatically curved rocker-bottom sole simulates walking barefoot on sand and engages core muscles. MBT, which stands for Masai Barefoot Technology, pioneered "natural instability." MBT shoes are the most researched; at least nine of the 39 studies have been published in peer-reviewed journals.
What we found: Walking in MBTs feels more like pushing off a rolling pin than shifting sand. Great for those who are on their feet all day; even yoga instructors are raving about them. If you have stability problems, try them in a safe place. Expensive and therapeutic-looking, but the best of the shoes we tried for serious instability. Not recommended for running.
Skechers Shape-ups XF: Extended Fitness for Women ($110, www.skechers.com)
About the shoe: Rocker-bottom curved sole simulates walking on soft sand. They come with an instructional DVD (start by walking in them 25 to 45 minutes a day) and a few exercises, which also can be done in traditional cushioned shoes.
What we found: Super-comfy and, unlike with the other brands, I was not embarrassed to wear these in public. The rocker bottom feels less curved than MBT; after a while they start to feel normal, which might diminish the effect. Priced in line with regular running shoes.
Reebok's RunTone ($100, www.reebok.com)
About the shoe: No visible rocker sole. Instead, "eight balance pods with moving air are built into the sole to increase energy absorption with every step," said John Lynch, head of U.S. marketing and merchandising for Reebok. "The effects are similar to running on a soft, sandy beach."
What we found: Springy, versatile, comfortable shoe that doesn't look like a "fitness" shoe. Will not throw you wildly off stride. Reebok's similar EasyTone, designed for walkers, features more instability than the RunTone. I used them for running, walking and strength training; simply wearing these made me want to work out more.
Trim treads ($39.99, trimtreads.com)
About the shoe: The severe cut of the shoe forces you to step on the ball of your foot, which might engage muscles in your legs, buttocks and core. The company says the shoes are similar to a combination workout on a bosu/balance board and a step machine.
What we found: Impossible to walk in. But if you can survive 30 minutes, your calves might hurt. Though designed by an OB-GYN to improve circulation in pregnant women, they take instability to a new level — which might not be what you want, especially if you're pregnant. Do not drive in these shoes or wear them in a wet area. Ugly, but a good way to get attention.
Fitflop Walkstar sandal ($49.95, fitflop.com)
About the shoe: The middle of the shoe contains what the company calls "muscle-loading micro wobbleboard midsole technology" to engage your muscles for a longer period as you walk. But there's no rigorous evidence showing they tone any better than other shoes or sandals.
What we found: Cushy and sporty, but I found them difficult to walk in. In fact, podiatrist Megan Leahy warns that "all flip-flops can exacerbate foot problems due to contractures of foot and toe muscles during gait in a subconscious attempt to keep the shoe on."