Her new DVD, Body Revolution, is for moms like her with no time. These are the core principles. By Marisa Fox, REDBOOK.

1. Circuit-train
Move from one strength-training exercise to another in an aerobic fashion. You'll give your muscles--but not your heart rate--time to recover.

2. Go for high-intensity intervals
Work out at 85 to 95 percent of your maximum heart rate for 20 to 60 seconds every few minutes. This helps you burn more calories overall. Sprint when you run, or jump rope during a strength circuit.

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3. Mix up your routine
Add yoga, boot-camp classes, kickboxing, or any new activity to keep your body from plateauing. You'll be fitter, stronger, more flexible, and better balanced.

4. Up the ante
Every two weeks, set new, harder goals. Reach for heavier free-weights, do more reps, or try push-ups on your hands and feet instead of your hands and knees. When you challenge your body, you continue to get new results.

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When I was younger I fantasized about what it would be like to have a personal trainer. Back then I thought they were only for the rich, but figured that if I could somehow afford one I'd have 6% body fat and arms like Madonna. Now that I'm older and have had a few personal trainers, I know that I was pretty clueless back then. Trainers aren't as expensive as I once thought, but if you aren't smart about how you use them they might as well cost a million bucks. Luckily for you, I have some advice on how to get your money's worth from a personal trainer.

Be Specific About What You Want
I hired my first trainer in the months leading up to my wedding. When the fitness manager at the gym asked me what I wanted to accomplish with a trainer, I said simply, "Well, I'm getting married…I'd like to be thinner, I guess." What I SHOULD have said was, "My dress really features my arms and back, so I'd like to work on toning them." My trainer had me do tons of cardio and almost no strength trainin

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