Shoemaker New Balance has been sued for false advertising over the company’s claims that its toning shoes tightened wearers’ butt and legs, and could increase calorie burn and muscle activation.

The suit, filed in Massachusetts federal court, seeks class action status and more than $5 million in damages.

New Balance offers a line of “toning” footwear with several products, including the “rock&tone” and “truebalance” shoes, which utilize a patented balance board technology that creates a destabilizing effect. Wearers must then engage core and lower body muscles to stay in balance, which New Balance claims results in muscle toning, additional calorie burning and weight loss.

But plaintiff Bistra Pashamova alleged in her suit that the company’s extensive, comprehensive national ad campaign made false claims comparing the toning shoes to traditional walking shoes. New Balance toning shoes “will result in 16% more activation to the gluteus, 16% more activation to the hamstrings, 14% more activation to the calves, [and] 29% more total muscle activation,” over traditional walking shoes, according to the suit, and the ads consistently stated the company’s claims were supported by scientific studies. Further claims include “Helping you tone up and slim down with every step” and “Tone muscles you didn’t even know you had.”

But the scientific tests were not subjected to traditional scientific study, according to the complaint, and were commissioned by New Balance. Independent testing found no statistically significant increase in either exercise response or muscle activation as a result of wearing toning shoes, the suit claims, and further, scientists have expressed concern that wearing toning shoes could lead to injury.

Pashamova seeks to certify a nationwide class for her claims of violation of Massachusetts state law.

To read the complaint in Pashamova v. New Balance, click here.

Why it matters: Toning shoes have become big business. The suit cites reports that retail sales of the product brought in $145 million in 2009, up from $17 million in 2008, and sales are expected to continue to increase in the coming years. Despite the profits – or perhaps because of them – manufacturers are now facing a number of suits over claims made about the benefits of the shoes, and the science that supports them. Last fall, three class actions were filed against Skechers, alleging that the company deceived consumers about the health benefits of its “Shape-up” line of toning shoes.