Grab a pair of light dumbbells and hold them at arm's length with your palms facing your thighs. Raise your upper arms so they're perpendicular to your torso and parallel to the floor. Bend your elbows 90 degrees, so that your forearms hand straight down toward the floor. Keep your elbows, wrists, ad upper arms in fixed positions, rotate the weights up and back as far as you can-you want your shoulders to act like hinges, your forearms like swinging gates. Pause, then return the forearms to the down position and repeat.