At a certain age, you stop playing. You stop swinging from monkey bars, racing your bike around the neighborhood, or bounding through sprinklers. Nowadays, you head to the gym where you follow a monotonous pattern of reps and sets, sit on a stationary bike, or race the clock to finish your workout. (Turn up your muscle gains outside the gym. These 18 Ways to Build Muscle All Day will help you shed fat, sculpt muscle, and accelerate recovery.)

This weekend, Todd Durkin, C.S.C.S., author of The IMPACT! Body Plan, wants you to start playing again. He's chosen two exercises that probably aren't part of your daily routine -- the broad jump and the bear crawl -- to create a fun (but super tough!) relay challenge. You'll ask your body to move in ways it hasn't moved in years for two minutes straight, taxing your muscles, generating sweat, and jolting your metabolic system.

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Watch the video above to see how to perform the challenge. Durkin completed 14 rounds of the relay in two minutes. Can your inner child beat Durkin's inner child? Let us know in the comments below. (Want to get the most from your workout? Then take the advice of this The Fitness Rule You Must Follow.)