Listen to this expert advice from a Celebrity Trainer, Ramona Braganza who trains Kate Beckinsale, "Combine interval and cardio circuit training for one hour. For instance: 10 minutes of cardio: Three sets of 15 to 20 reps of three different strength exercises, like ones that work the chest, quads, and triceps. 10 minutes of cardio: Three sets of 15 to 20 reps of three different strength exercises, like ones that work the back, hamstrings and biceps."