6. BOSU trainer
Short for “both sides up,” the BOSU trainer provides two types of workouts from one piece of gear. Use either side to make upper body exercises–such as pushups, planks, or other abs movements–more difficult by adding instability and forcing your muscles to work harder. But be wary of standing on the ball for exercises–research shows that doing exercises on one leg is a better (and safer) way to build balance and stability. All together, you’ll work your body harder without adding weight.