When doing the lateral arm raise, coaches and trainers recommend raising the arms only to the level position. However, stopping when the arms are horizontal can create tightness in the shoulder and may lead to shoulder impingement.
Typically the arms are raised only to shoulder level (90 degrees) because of the relatively heavy weights that are usually used in this exercise. But, for full range development of the targeted deltoid muscle, you must raise the arms completely overhead.
The deltoid is most active and undergoes greatest tension from the shoulder level position to the completely overhead (180 degrees) position. The overhead movement helps to maintain or create greater flexibility in the shoulder joints, which is extremely important not only for bodybuilders, but for all athletes.
To gain flexibility and strength through the full range of motion, you have to use less weight in comparison to going only to the level arm position. Going full range will give you greater definition not only of the deltoid but the upper and lower divisions of the trapezius together with better joint safety.
Execution
To execute, hold the dumbbells alongside the body, and maintain an erect standing position. When you are ready, inhale slightly more than usual and then hold your breath as you raise your arms up and out to the sides, making sure to keep them straight (but not locked) until they are well above the shoulders (or as far as your flexibility will allow).
Your trunk should be maintained in a normal upright position throughout the movement. After reaching the uppermost position, relax your muscles slightly and exhale as you return the weights under control back to the original position.
Be sure to maintain a neutral grip, ie, so that shaft of the dumbbell points forward and backward throughout the execution. The thumb side of the hand should remain facing forward, or you can rotate the arms laterally so that the little fingers end up pointing forward in the top position.
If you do the exercise with a pronated grip (with the arm rotated inward), you will only be able to raise the arms to shoulder level since the inward rotation blocks the humerus from moving freely in the shoulder joint. The pronated grip targets mainly the supraspinatus not the deltoid.
The lateral dumbbell arm raise is very important for all athletes, especially for those who must continually raise their arms overhead. For more information on this and other exercises, see the books Kinesiology of Exercise and Build a Better Athlete. Also see the CD’s Kinesiology — Student and Teachers Edition and Kinesiology Standard Edition and the DVD, Exercise Mastery.