The single-side bird dog exercise looks easy, but don’t be fooled: It’s ridiculously hard. In fact, about 99 percent of people can’t do it, says Sam Stauffer, a trainer with Men’s Health Thrive in Philadelphia.

What makes the move so challenging? You start on all fours, but lose two bases of support when you pick up an arm and leg on the same side. “When you take away your arm and leg, your core stabilizers must work overtime to keep you from falling over,” says Stauffer. “Many of us don’t train for this type of core stability, so we can’t hold this position.”

But you should start training your middle this way. "Almost every movement in daily life involves core stability," says Stauffer. “The better yours is, the stronger you'll be in everything you do. Plus, if you don’t have it, you’re likely to overcompensate with your lower back, which can contribute to back pain.” (Think you have the pushup down? Think again. Here are 5 Body-Weight Exercises You're Doing Wrong.)

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

Start to build your core stability with the plank position row. It trains your midsection to resist against rotation, flexion, and extension when you lift up a base of support. Watch the video above to see Stauffer perform the exercise with perfect form. Do one set of 8 to 12 reps on each side with a heavy dumbell two or three times a week. If you follow this routine, you should notice a significant improvement in your ability to do the single-side bird dog in about 4 weeks.

The only training manual you need to bulk up fast!