Sculpt a crazy-hot body with this double-dip trick: Just adding water will turn up the firming and burning power on your rep-ertoire. Why fry in scorching summer temps when the fastest way to rock a cute suit is to tone below the water's surface? "The key is that water offers heavy resistance," says Igor Porciuncula, the cofounder of Boot Camp H20 in Los Angeles -- 12 times the resistance of air to be exact. That means your moves engage more muscle fibers and burn more calories in a shorter amount of time. Snag a kickboard from poolside and do Porciuncula's shape-and-shred circuit twice through for sexy arms, tight abs, trim thighs, and zero dripping sweat.