How long does it take to get in a great cardio workout? Not as long as you might think. That is, unless you think the answer is four minutes.

Seriously.

Our proof: The fast and furious routines that follow, courtesy of fitness expert BJ Gaddour, CSCS, owner of StreamFIT.com -- a web site that offers follow-along, bootcamp-style workouts (that you can stream to your TV, tablet, smartphone, or computer). These 4-minute workouts are all based on the "Tabata protocol."

For background, the Tabata protocol is a training method that was originally used by the Japanese Olympic speed skating team, and named for the scientist -- Izumi Tabata -- who studied its amazing effect on a group of male college students. The study subjects were all fit P.E. majors, and most were members of various varsity sports teams.

You might think it sounds too simple -- and short -- to work: On a stationary bike, the university students did seven to eight 20-second, all-out sprints, each separated by just 10 seconds of rest. Total time: 4 minutes. (They also did an easy 10-minute warmup before each session.)

The results were fantastic: After doing the routine 5 days a week for 6 weeks, the college kids boosted their aerobic fitness by 14 percent. By comparison, another group -- who performed a steady but moderate pace on the bikes for 60 minutes -- increased their aerobic fitness by only about 10 percent. (If you want more fast cardio and fat-loss workouts, along with full-color photos of more than 600 exercises, check out my books, The Men's Health Big Book of Exercises and The Women's Health Big Book of Exercises.)

The upshot: The high-intensity 4-minute workout was more effective than an hour of moderate cycling. Even better, the Tabata participants saw a 28-percent improvement in "anaerobic capacity" -- a measure of how long the men could exercise at their top effort. The second group saw no such improvements.

So why isn’t everyone doing Tabata workouts? Well, many people would get nauseous if they actually tried the routine that was used in the study. That's not good. Plus, to burn as many calories as you might like, you need to regularly exercise longer than just 4 minutes. (The study participants literally exercised themselves to exhaustion, making additional work unlikely.)

The good news: Gaddour has a way to solve both problems -- while also making the Tabata method even more beneficial.

Instead of doing a single mode of exercise for each sprint, Gaddour alternates between two body-weight exercises that work your muscles in different ways. This way, fatigue doesn’t overtake you as quickly -- such as was the case with the stationary bike. So you’re still working hard for each 20-second interval, but you’re spreading the challenge around. (Is your workout dangerous? Find out by reading my new story, America's Scariest Fitness Trends.)

Will it improve your fitness as fast as it did for the Japanese college students? No one knows. But you’ll no doubt find it highly effective. "Whether you’re short on time and need a quick workout, or just want to add some extra intensity to the end of a longer session, one of these 4-minute routines will do the trick," says Gaddour, who calls each mini-workout a 'finisher,' since he often ends his fitness bootcamps with them.

There’s more: Because this style of Tabata training allows you to better manage your fatigue, you can "stack" multiple 4-minute routines together. The key is to simply take 1 minute of rest between every 4-minute mini-workout. This way, you’re able to recover briefly between routines, and give it your all each time -- while creating a longer workout for greater calorie-burn. And by stacking these routines, you can choose exercises that work your muscles and joints in multiple directions -- which helps you build a stronger, more fit body.

Ready to get started? Check out the three 4-minute finishers below. Gaddour refers to them as "cardio-core" routines because each combines a total-body calisthenic with a cutting-edge core exercise. "The cardio exercise burns the fat covering your belly, while the core exercise strengthens and tightens up your midsection," says Gaddour. "That makes it a fantastic one-two punch for achieving flat, sexy abs." (Speaking of flat, sexy abs, make sure to check out this list of The 100 Hottest Women of All-Time.)

How to do the workouts: Choose one finisher and perform the first exercise for 20 seconds. Then rest for 10 seconds. Do the second exercise for 20 seconds, and rest for another 10 seconds. Continue to alternate back and forth for 4 minutes -- a total of eight 20-second intervals. That’s it!

If you want an even greater challenge, simply do Finisher #1 for 4 minutes, then rest 1 minute. Next, do Finisher #2 for 4 minutes. Rest for another minute, and do Finisher #3 for 4 minutes. Do the math: That’s a 14-minute high-intensity cardio workout. It’s guaranteed to blast fat, boost your fitness, and get you in shape in (almost) no time.

Finisher #1
Exercise 1: Stationary running
Exercise 2: Mountain climber

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Finisher #2
Exercise 1: Seal jacks
Exercise 2: Push-up jacks
(Note: If you haven’t ever seen a pushup jack, you must check out the video. It’s an awesome and unusual variation of the push-up.)

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Finisher #3
Exercise 1: Skater jumps
Exercise 2: Plank to push-up

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One more thing: Have fun! And if you want to reveal your six-pack in 2012, make sure to discover the Amazing Ab Secrets You Need To Know.)

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