Ab gizmos can be a waste, study finds.(The Dallas Morning News)

Quick _ if you could tone up just one part of your body, which would it be?

Odds are it's your abdomen.

"It's one of the few areas where, across the population, people recognize the importance," says Dr. Peter Francis, director of the biomechanics laboratory at San Diego State University.

"If you're young and cute, those flat abs are fun to look at. If you're physically active, abs are very important mechanically," he says.

"And as people age, they realize that low back pain is part of the human condition, and people say, `You've got to strengthen those abdominals.'"

Retailers bought about $125 million in abdominal exercisers from wholesalers in 1999, according to the Sporting Goods Manufacturers Association.

But when Francis studied what type of exercise really works the abs, he found that the type of gizmo you see on infomercials isn't the way to go.