You might remember the dragon flag from the Rocky IV training montage. Rocky Balboa laid on a bench, and then lifted and lowered his feet, legs, butt, and torso in one straight line. It makes your abs burn just watching it. But then we saw Josh Halbert, Director of Education at Kinetic Systems Strength and Conditioning in Columbia, Maryland, do the walking version of the exercise. Suddenly, the dragon flag didn't look so tough. Check out the video below to see him perform the move.

"Just like the dragon flag, the move requires extreme core strength," says Halbert. However, "walking" your legs during the movement requires every last stabilizing muscle in your body to fire. The reason: You not only have to resist your back from sagging or bowing, but you also have to stop your body from tipping side to side, he says. (Carve the invincible abs you've always wanted in as little as 2 hours a week with The New Rules of Lifting for Abs.)

Think about the move as an upside-down plank: While holding a plank position, your glutes, quads, and core are braced as one solid unit. The second you pick up one foot from the floor, though, the move instantly becomes more difficult. The muscles that are still involved must work even harder to maintain the same rigid, straight torso you had before.

To prepare your body for the challenge, start with an exercise called Rocky Abs, seen in the video below. It focuses on the eccentric, or lowering, portion of the movement. Your muscles can handle more weight on that phase of a lift, but slowing the pace forces your muscles to work harder. Once you master that, add in the "walking" leg movements. (Reveal the abs you never knew you had with the 6 Moves for a Six-Pack.)

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