Begin on hands and knees ("all fours") with a dumbbell in one hand. Knees should be directly under the hips, about shoulder width apart. The hands and dumbbell should be directly under the shoulders. With a neutral grip (palms facing in), raise the arm holding the dumbbell up so that the upper arm is parallel to the floor (elbow should be at a 90 degree angle with fist pointing down). Engage abdominals and pull navel in to stabilize your core. Maintain a neutral (flat to normal) spine. While maintaining this upper arm position, exhale and forcefully extend your forearm up until entire arm is straight and parallel to the floor. Pause then slowly lower forearm back down without lowering the upper arm. Repeat using other arm.