Grab a pair of dumbbells and lie back on a flat bench. Position the dumbbells so they are above your shoulders with your arms fully extended and palms facing each other.
Start by lowering the right dumbbell first. Bring the right dumbbell to the side of your chest, and then press it back to the starting position. Make sure your left arm stays fully extended as the right dumbbell moves.
Switch sides and use the left arm to repeat the same motion while keeping the right arm straight.
Control the movement, keeping your chest up and shoulders back and down the entire time.
One full rep with each arm counts as one total repetition.