No weights, no nonsense. "You don't need dumbbells, barbells or machines to prove you're fit," says Todd Durkin, C.S.C.S., author of The IMPACT! Body Plan. "When you're on the road or don't have access to a gym, your own weight provides more than enough resistance to give you a hard-core workout."

Use nature's best barbell -- your own body -- for this weekend's fitness challenge. You'll perform three moves -- the burpee to broad jump, the bicycle crunch, and the cross-body mountain climber -- back-to-back-to-back with no rest. "You'll work your muscles from head to toe and sweat buckets while doing it," says Durkin. (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.)

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Are you ready to try it? Durkin completed two round of the challenge in one minute and 59 seconds. Let us know your time in the comments below.

Beat your workout plateaus with this 5-move Total-Body Muscle Assault.