There's a reason why every celebrity in Hollywood is lacing up her boxing gloves -- and it has nothing to do with training for a role inside the ring. According to Jeff Hunter, the face of boxing apparel brand Everlast and a trainer at YG Studios, boxing is the single-most effective way to tone the entire body and torch massive amounts of fat in a hurry. According to Hunter you can burn anywhere between 500 to 700 calories in a single 20-minute boxing session (as long as you're giving it 100 percent, of course).

"This high intensity interval training combines your cardio and resistance training, and it's not as monotonous as traditional exercise can sometimes be," says Hunter. "Look at any body of a boxer and they're very lean and muscular. It's an amazing and effective workout." No wonder supermodels like Gigi and Gisele are stepping away from the yoga mat and into the ring.

It also doesn't hurt that it's a healthy way to blow off steam. Even Gwyneth Paltrow, queen of all things serene, says she throws punches regularly in order to "experience aggression."

So wrap your wrists and lace up your gloves, ladies. This 20-minute boxing workout, designed by Hunter, will get you shredded and burn off any bad day.

Before you're able to go all "Million Dollar Baby" on your workout, you need to master a few boxing basics.

To start, arm yourself with the right equipment. You'll need boxing wraps and punching gloves (check with your gym to see if they carry any), which will help ward off injury, support your wrists and make you look pretty badass. If your current wardrobe does not include boxing gloves, don't sweat it (yet). All these exercises can be modified into a shadow boxing routine (you'll punch the air), which is just as effective.

Next, assume the position -- the proper boxing stance, that is.

1. Stand with your feet slightly wider than your hips.

2. Step your dominant foot behind you, slightly turning it away from your body. Place your other foot straight in front of you.

3. Now that you've got your foot placement down, point your left shoulder at the punching bag and hold both your hands near your cheek bones, while keeping your elbows close to your body and your hands in relaxed fists.

Throughout this workout, you will be alternating arms, so you'll be switching up your stance. When you punch with your left fist, your right shoulder should face the punching bag, and your left foot should be behind you. When you punch with your left fist, your left shoulder should face the punching bag, and your right foot should be behind you.

Got it? Now you're ready to kick some serious butt (even if it's only your own).

It's time to start throwing punches. Jabs will give you the lean, sculpted arms and shoulders of your dreams. Oh, and you'll definitely boost your heart rate as you're going ham on the punching bag.

1. Start in a boxing stance with your hands to your cheeks, elbows in, and legs slightly bent.

2. Step forward. Using your back leg for power, extend your left arm, and hit the with the knuckles of your index and middle fingers. Be careful not to twist your hips.

3. Jab for a minute and a half on your left side, and a minute and a half on your right. Rest for a minute before continuing on to the next move.

Your heart rate should be elevated at this point, which means your metabolism is starting to torch that unwanted fat. "Anything that spikes your heart rate and then levels out, is going to speed up your metabolism," Hunter says. "But it's very important to get that one-minute rest. It confuses the body, which will keep it burning the fat."

Think of this move as a jab with a twist.

1. Start in the boxing stance, with your hands to your cheeks, elbows in and legs slightly bent.

2. Much like throwing a ball, turn your hip inward as you extend your right arm, again hitting the bag with your first two knuckles.

3. Jab with each arm for a minute and a half. Then rest for a minute before jumping into the next move.

If you find yourself in a seriously aggressive mood, a hook will help you work out all that anger.

1. Start in the proper boxing stance (as usual).

2. Pivot your left leg and hip away from your body as you throw your punch.

3. When you throw your punch, make sure your forearm is parallel to the ground and your arm comes across your body. Your bent arm will resemble a hook -- hence the name of this move.

4. Now do steps two and three simultaneously.

5. Repeat a series of hooks for three minutes straight alternating arms (1:30 on each side), followed by a one-minute rest.

If you're dying a little bit at this point, you're doing it right.