Grasp dumbbells to each side. Bend knees and bend over through hips with back flat, close to horizontal. Position elbows with slight bend and palms facing together.
Raise upper arms to sides until elbows are shoulder height. Maintain upper arms perpendicular to torso and fixed elbow position (10° to 30° angle) throughout exercise. Maintain height of elbows above wrists by raising "pinkie finger" side up. Lower and repeat.
Dumbbells are raised by shoulder transverse abduction, not external rotation, nor extension. Upper arm should travel in perpendicular path to torso to minimize relatively powerful latissimus dorsi involvement. In other words, at top of movement, elbows (not necessarily dumbbells) should be directly lateral to shoulders since elbows are slightly bent forward.
To exercise posterior deltoid and not lateral deltoid, keep torso close to horizontal. Positioning torso at 45° is not sufficient angle to target rear deltoids. Knees are bent in effort to keep low back straight (See Hamstring Inflexibility). If low back becomes rounded due to tight hamstrings, either knees should be bent more or torso may not be positioned as low. If low back is rounded due to poor form, slowly lower torso into horizontal position with knees bent and back straight. Also see Rear Lateral Raise Errors.