Step by step instructions
Grab a dumbbell in left hand and get into a side plank, propping upper body up on right elbow and forearm. Bend bottom knee for support and raise hips until body forms a straight line from ankles to shoulders. Extend left arm up to ceiling above shoulder, looking up at hand.
Keeping hips steady and abs drawn in tight, reach under and behind torso with left hand (eyes should follow left hand), then lift arm back to the starting position. That's one rep. Do all reps on the right, then repeat on opposite side to complete the set.