They are, advertisements say, a game-changer in athletic footwear: sneakers that are supposed to tone muscles, promote healthy weight loss and improve the posture of those who walk, work or shop in them.

The makers of "toning shoes" say the shoes can help give wearers more shapely butts, legs and abs, often without the need for gym workouts. That's partly why toning shoes — which often have a rounded sole like a rocking chair, to stretch the wearer's leg muscles with each stride — represent the fastest-growing segment of the $17 billion-a-year athletic footwear industry. It's a market driven by a customer base that is 90% women, according to sneaker analyst Matt Powell of SportsOneSource.