A kettlebell is one of the most efficient, effective tools for sculpting a slim, strong physique. Why? Instead of isolating muscle groups like you do when lifting dumbbells, you work all your major muscle groups at once with a kettlebell. That's because the weight isn't evenly distributed, so you have to work continuously to control the bell's shifting center of gravity. The result: major calorie burn—a recent study by the American Council on Exercise found that kettlebell exercises can burn up to 20 calories a minute—while you add definition to your shoulders, back, butt, core, and arms.
How it works: Three days a week, perform 1 set of each exercise back to back. Do the entire circuit 3 times. For best results, schedule your workouts on non-consecutive days so your body has time to recover.