If you want more of a challenge, do this exercise with a dumbbell or medicine ball — you'll definitely feel the burn.
"Start by sitting on your butt and leaning back until you feel your abs engage. (Important: keep your feet pinned to the ground! This will help make sure your core is engaged," Garzo explained.)
"Reach down to one side with both hands (or weight, if you're using one) then rotate up to the opposite side as if you were drawing a diagonal line from your hip to the sky," she said.