Start in a forearm plank position, arms stacked horizontally beneath your shoulders, core engaged. Place your dumbbell on the right side of your body, outside of your right elbow. Then, reach your left arm underneath your body to grab the dumbbell in your left hand, before pulling it across the mat, setting it outside the left side of your body. Return your left hand to the mat, returning to the starting position. Repeat on the other side.