Completing 110 burpees in a row is extremely difficult. Doing them on one leg at a time in a suspension trainer -- as this week's challenge requires -- will make your muscles scream and test your willpower. The instability of the TRX makes it tough to stabilize your body throughout the movement, says Pete Holman, PT, C.S.C.S., director of Rip Training at TRX. You must activate more muscles and work harder to maintain proper form during each rep. (Try these 5 Secrets to the Perfect Workout and you'll never be held back in the gym again!)

That's why cranking out 110 reps requires an insane amount of athleticism and total-body stability. If you can reach that goal, you'll know your body is primed for peak performance at the Men's Health Urbanathlon, a 10- to 12-mile run that's filled with crazy barriers (taxi pileup, anyone?). "You'll have no trouble crawling under obstacles or jumping over them, and sprinting your way to a fantastic finish at the race," says Holman.

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Didn't reach 110 reps? Don't worry: Click here to get a full TRX Urbanathlon training plan. It'll prepare your body for race day and get you in the best shape of your life.

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