If you want to drop pounds and shrink your waistline, skip the dumbbells and head straight for the StairMaster. A new study shows that cardio trumps weightlifting when it comes to shedding fat and reducing total body mass. Researchers at Duke University Medical Center put 119 overweight adults on a three-times-a-week regimen of either intense aerobic exercise for 45 minutes, resistance training, or both for eight months. At trial's end, both the aerobic and aerobic-plus-resistance groups lost weight and body mass and shaved inches off their midsections. However, the combination group didn't lose any more than the aerobics-only participants, even though their workout took twice the time commitment. And as for the weights-only group, its members didn't get lighter or smaller – only stronger.

Of course, there's nothing wrong with building strength by packing on lean muscle mass, if that's your goal, but study author Cris Slentz says that if your mission is to lose weight, then cardio's the way to go. Plus, he points to overwhelming evidence that fat-melting aerobic training reduces the risk of cancer, heart disease, diabetes, and more, whereas resistance training alone hasn't been shown to have these benefits.

If you have hours to whittle away at the health club, then by all means bust a lung and lift to reap the rewards of both. But if you're like most, then your time is limited and precious, so run, cycle, or step your way to a slimmer physique.