The U.S. Consumer Product Safety Commission has issued a warning to consumers to stop using certain Sperax walking pads and treadmills, popular fitness products sold at retailers such as Walmart. The agency has received hundreds of reports of sudden speed changes, abrupt stops, overheating and fires, resulting in at least 66 reported falls or injuries. The products were manufactured in China and marketed under the Sperex brand. The CPSC has not yet issued a recall.