Jumping jacks are a great calisthenic, but they hardly scream, "This is going to be a brutal workout!" That's about to change. For this weekend's Train for Life challenge, kick up the intensity of this old-school exercise by performing a terrible trifecta of push-up jacks, squat jacks, and seal jacks. "These variations of the classic jumping jack will get your muscles burning and your heart pumping in no time," says BJ Gaddour, C.S.C.S., metabolic training expert who designed the Men's Health Speed Shred DVD Series and owner of StreamFit.com.

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Perform 11 push-up jacks, 22 squat jacks and 33 seal jacks in a row. Then repeat. Test yourself by doing two rounds as fast as you can. Rest whenever you want, but keep the clock running the whole time. If that’s too difficult, try the modified challenge by removing the push-up from the pushup jack. Make sure your pushup form is correct for the best results. Click here to find out Are You Doing Push-Ups Wrong?

Push-Up Jack

Assume a pushup position, your hands slightly beyond shoulder width. Your body should form a straight line from your head to your ankles. Jump your hands and feet out a few inches wider, while bending your elbows and lowering your body until your chest nearly touches the floor. Then push up with enough force for your hands and feet to come off the floor. Land in the starting position. That is 1 rep. Do 11.

Squat Jack

Stand with your feet together and your hands at your sides. This is your starting position. Jump your feet out to shoulder-width apart and lower down into a squat, reaching your arms straight out in front of your body at shoulder level. Immediately jump back up to the starting position. That's 1 rep. Do 22 total. For more new exercises from the country’s leading experts, sign up for the Exercise of the Week newsletter.

Seal Jack

Stand with your feet together. Your arms should be straight out in front of your body at shoulder level and your palms together. Simultaneously squeeze your shoulder blades together, pull your arms out to your sides (they should still be parallel to the floor), and jump up just enough to kick your feet out wide. Without pausing, quickly reverse the movement and repeat. That's 1 rep. Do 33 reps.

Are you fit enough to beat BJ or Jill? Watch the video above to see them perform the Get Jacked Up challenge.

BJ finished 2 advanced rounds in 2 minutes and 14 seconds, and Jill completed 2 modified rounds in 2:09 seconds. What was your time? Let us know in the comments below, and click here for more FREE workouts from the experts at Men's Health!