Rowing Machines
Credit: Photograph by Terrence Darvin

Also known as ergo­meters, these engage so many muscles at once, while also taxing the cardiovascular system, that they provide a better warm-up than a treadmill or a jump rope. "You can place a tremendous demand on the whole system," says Mark Merchant. "And when coupled with two or three full-body strength movements – say, a front squat, a burpee, and a press – they're great for circuits. Just 20 minutes will smoke you."