Leave the crunching to the accountants this tax season. "If you want to reveal your six-pack, you need to blast your abs and strip away the fat that covers them," says BJ Gaddour, C.S.C.S., metabolic training expert and creator of The Incredible 82-Day Speed Shred. One of the best ways to do that: mountain climbers, which strengthen your entire core and send your metabolism through the roof. That’s why today's Train For Life challenge includes five -- yes, five! -- demanding variations of the the exercise. Each version is harder than the next. Will you make it to the summit of Mount Metabolism?

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Here's how it works: You'll perform 20 reps of a mountain climber variation, and then move on to the next variation. Continue like this until you’ve finished all five variations.

1. Mountain Climber
Assume a standard pushup position. In one smooth motion, bring your right knee toward the right side of your chest. Then bring your left leg forward while extending your right leg back. Avoid any lower back movement throughout the exercise. Continue alternating your knees to your chest. Do 20 reps.

2. Spider Climber
Assume a standard pushup position. In one smooth motion, bring your right foot to the outside of your right hand. Then bring your left foot forward next to your left hand while extending your right leg back. Continue to in an alternating fashion for 20 reps.

3. Diagonal Mountain Climber
Perform a standard mountain climber, but bring your knees to your left elbow with each rep. Do 10 reps. Repeat with the right elbow.

4. Cross-Body Climber
Perform a standard mountain climber, but bring your right knee toward your opposite (left) elbow. Then bring your left knee toward your right elbow while extending your right leg back. Continue alternating for 20 reps.

5. Side-to-Side Climber
Get down on your hands and knees. With your back straight, fully extend your right leg to your side until it is forms a 45-degree angle to your body. Lift your left knee a couple inches off the ground. This is the starting position. In one smooth movement, switch your leg positions so your right knee is hovering above the floor and your left leg is extended to your side. That's 1 rep. Continue to alternate back and forth for 20 reps.

Ready to climb Mount Metabolism? Watch the video above to see BJ and Jill demonstrate all five mountain climber variations.

BJ finished the challenge in 1 minute and 21 seconds, and Jill completed it in 2 minutes and 9 seconds. What was your time? Let us know in the comments below.

(Need more of a challenge? Follow along with Gaddour in the new DVD series from Men's Health, Speed Shred.)

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