Step by step instructions
Stand with feet hip-width apart, abs braced in tight to spine, holding one end of an anchored resistance band with arms extended in front of chest. (Band should be positioned at abs level to the left of body; anchor it securely around a doorknob or similar object.)
Without moving torso or hips, quickly move arms left to right and back to starting position without moving past the side of torso. Position band to the right of body and repeat to complete set.