Quick — 10 minutes, that's all we've got. But fret not, sweat plenty, that's all the time you'll need to squeeze in a rat-a-tat whole-body workout.

So says exercise physiologist Sean Foy, longtime personal trainer and author of "The 10-Minute Total Body Breakthrough" (Workman Publishing, $22.95; 4321fitness.com).

This whole-body blitz adds up like this:

Four minutes, high-energy aerobic training.

Three minutes, resistance exercise.

Two minutes, core strengthening.

One minute, stretching and deep breathing.

According to Foy, who practices in sunny Southern California (but of course), the 4-3-2-1 equation will have you burning fat, building muscle and generally catapulting yourself into higher gear.

Of course, we had only 10 minutes to talk to the fast-moving Foy, so we set the clock and fired away.

Here's how it flew:

QUESTION: Why is 10 better than nothing?ANSWER: Most Americans are doing nothing. You know what happens when we do nothing? Our muscles atrophy. (That means they basically waste away and shrink down to nothing.) The No. 1 excuse for not doing anything is time. So here's all you need to do in 10 minutes.

QUESTION: So is this some kind of trick — you hook us on 10, only to find out down the road that it won't make a difference until we work up to 60?ANSWER: No, no, it's not a trick. If you did one minute, it's better than nothing. Ultimately, 10 minutes is a complete circuit. We'd love it if you'd do two cycles, or three cycles. For years, the American College of Sports Medicine has been saying three to five days a week, do 20 to 60 minutes of aerobics, two to three days of resistance training, every day stretching. But the dilemma here is that no one's doing it. Our challenge is to get 10 million people doing 10 minutes a day.

QUESTION: What's the magic behind the 4-3-2-1?ANSWER: You need to do the circuit without taking a break. With no rest!Researchers have found that it's the interval — switching from 30 seconds of moderate intensity to 30 seconds of high intensity — that boosts your metabolism.You'll burn more fat and burn it for longer after the workout. That's called the afterburn.

QUESTION: When's the best time for the workout?ANSWER: I always say, "The best time to do the workout is the time you'll do it." Studies, though, do show better adherence to an exercise routine when you do it first thing in the morning.

QUESTION: What's the most important thing we need to know about nutrition?ANSWER: Don't diet. Diet is deprivation, inadequate nutrition, excessive and tedious. I'm all for the no-diet diet. I call it the "Traffic Light" approach: Green foods — fruits and vegetables and water — are "Go;" yellow foods — nuts, whole grain carbohydrates, lean proteins — are "Slow Down;" red foods — sugars, fats and alcohol — are "Stop."

QUESTION: What else do I need to know?ANSWER: Read the book.