Toning shoes have an unstable design—either a uniquely rounded sole or rounded pods built into the front and heel of the shoes and extra cushioning. This design deliberately forces you to struggle to maintain equilibrium with each step. They’re also about 4 to 7 ounces heavier than traditional running shoes.

The payoff? Their instability will supposedly make your leg muscles work harder and, along with the added weight, up your calorie burn.

It makes sense, which may explain why toning shoes are all the rage. But a pair of studies funded by the American Council on Exercise (ACE) and carried out by University of Wisconsin–La Crosse exercise physiologists found that none of the toning shoes tested (Skechers Shape-Ups, MBT, and Reebok EasyTone) performed any differently than regular running shoes.

In the studies, 24 physically active women, ages 19 to 27, each completed a dozen exercise trials in which they walked on a treadmill for five minutes wearing each type of shoe in random order. The result? “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,” ACE concluded."