The Workout

You will need: Two to three sets of dumbbells, and a stopwatch or a clock or watch with a second hand. The workout will take you 20 to 45 minutes, depending on your level and the length of your warmup and cooldown. And depending on which level of workout you do, you'll burn between 200 and 440 calories per session.

Warm up: Do 3 to 5 minutes of easy cardio. Examples: Marching in place, jump rope without rope and super-slow jacks.

Workout: Alternate a cardio interval with one strength-training exercise. Take little or no rest in between cardio and weight-training intervals. Your goal is to keep your heart pumping, your body moving and the calories melting away.

• Beginners: Do one round of the circuit, doing the version of the exercises aimed at your level. Do 1 minute of each cardio interval and 12 repetitions of each strength move.
• Intermediates: Do one round of the circuit, doing the version of the exercises aimed at your level. Do 90 seconds of each cardio interval and 15 repetitions of each strength move.
• Advanced: Do two rounds of the circuit, doing the version of the exercises aimed at your level. Do 90 seconds of each cardio interval and 15 repetitions of each strength move.

Cooldown: Repeat warmup.