This is one of the most challenging ways to work your abs! Your entire core has to engage to perform weighted rows from this plank position.
How to do it: Start in a full plank position with feet hip-width apart, hands on top of dumbbells. Brace your abs in tight and row your left arm back, pulling the dumbbell to the side of your body. Gently lower arm and repeat on the right. That's one rep. Do up to 3 sets of 10 repetitions.