Excuse: "I don't see results, so what's the point?"
Breezing through the same 30-minute routine day after day isn't going to transform your shape, says trainer Gunnar Peterson. Your body gets efficient at fat storage, so unless you trick it, it's not going to let go. "The most effective way to burn fat is by interval training," says Michelle Lovitt, who trains Julianne Moore. "Do short segments of speed work, recover, then get your heart rate back up again." To get an accurate read, the Polar F6 monitor can tell you whether you're in the fat-burning zone.