Sit on the edge of a flat bench with dumbbells on your knees. In one smooth motion, roll onto your back while bringing the dumbbells up to a position slightly outside and above your shoulders. Your palm should face forwards. Bend your elbows at a 90 degree angle so that your upper arms are parallel to the ground. Press the weights up over your chest in a triangular motion until they meet above the centerline of your body. As you lift, concentrate on keeping the weights balanced and under control. Then, follow the same path downward until your arms are slightly below parallel to the floor.