Look 10 Years Thinner With This Workout

Credit: David Martinez

Build muscle fast

Follow this simple 20-minute routine five times a week, for three weeks. It alternates high-intensity cardio-and-strength moves to maximize calorie afterburn with more restful strength-only exercises that help boost your metabolism.

Do it straight through (don't rest in between exercises). Not feeling challenged? Just add weight or increase your reps.

Next: Step-ups