A new lawsuit alleges that Skecher's Shape-up shoes can cause serious injuries.
An Ohio woman is suing the company after developing stress fractures in both hips -- which she blames on the shoes.
Skecher's Shape-ups have a distinctive round sole. They are marketed as toning shoes, the fastest-growing segment of the athletic shoe market.
Toning shoes are meant to help you get in shape as you walk or work. But at least one person says rather than helping them, the shoes hurt them.
Holly Ward, 38, says her routine involves physical therapy and she now has pins in her hips because of injuries she says were caused by wearing Skecher's Shape-ups.
"The extended use of these shoes has injured me catastrophically," Ward told "Good Morning America."
Shape-ups are advertised as helping you get in shape and helping reduce pain. Kim Kardashian and former NFL quarterback Joe Montana have appeared in commercials for Shape-ups.
Ward says she wore the shoes during her work as a waitress and while on walks and developed severe pain after five months. According to her lawsuit, she had fractures in both hips near where they meet the thigh bones even though she has the healthy bone density of a young woman.
"The femoral bone is the strongest bone in the human body and I fractured not one but two of them without being in a car crash or any traumatic incident," she said.
Skechers and its critics do agree on one thing: Shape-ups shoes change the way you walk.
A Skechers training video advises wearers to "step forward with the middle section of your heel hitting the ground first. Roll forward onto the ball of your foot and push off with your toes."
Company Says Millions Wear Shape-Ups Without Problems
The company calls its shoes revolutionary. Ward's lawyer calls them dangerous.
"We do not know of any testing or safety studies that Skechers did to determine safety," said Ronald Johnson, Ward's attorney. "If they're going to invent a whole new way for a human being to walk, the very first thing they should do is studies to make sure that's not going to harm their customers."
Ward says the potential gain is not worth the potential risk.
ABC spoke to half a dozen orthopedists and most were skeptical that shoes alone could cause stress fractures.
Skechers told ABC that "since this lawsuit is brand new, we have not had an opportunity to review Ms. Ward's allegations … millions of people wear Shape-ups without experiencing what Ms. Ward alleges."
Ward's lawyer says he has heard from more people with fractures.
And published reports quoting doctors who say they've seen other injuries like strained Achilles tendons and falls because people lost their balance. Skechers tells people to start wearing the shoes gradually to get used to them and avoid injuries.