Many guys develop a decent set of anterior (front) deltoid muscles, just from doing enough chest work. However, you’ll never max out your physique development and reach the height of muscle symmetry if you have flat, underdeveloped side (medial) deltoids sitting on your shoulders. Generally, the medial fibers of the deltoid do not get enough stimulation to get that round, full appearance from basic exercises alone. Nevertheless, this is fixable – but you must be willing to train with fire-blazing muscle tension to build the medial part of the deltoid.

If you thicken the medial part of the deltoid, your upper back and chest will look wider from the front, even when relaxed. Furthermore, thick medial deltoids will improve your symmetry, because your waist will look smaller. Seated dumbbell lateral raises are excellent for adding shape and size to the deltoids, without overly stressing the shoulder joint.

Overview of the Deltoid Muscle

The deltoid muscle caps five other muscles and the bony connections, which make up the shoulder joint. This deltoid has muscle sections that arise from three different bony regions on the shoulder girdle. The anterior fibers of the deltoid attach between the lateral part of the clavicle and the humerus bones. The anterior fibers flex the humerus at the shoulder (bringing the humerus bone of the upper arm forward), and also medially (internally) rotate the humerus at the shoulder. The posterior fibers of the deltoid originate from the inferior edge of the spine of the scapula, and insert at the lateral (outside) of the humerous bone (upper arm). These fibers extend the humerus (pull the arm backward). The medial fibers of the deltoid are primarily activated by seated lateral raises. They connect the acromion of the scapula and the humerus bone. Although weight trainers call this the lateral portion of the deltoid, these fibers are anatomically located in the medial region of the deltoid (with respect to the other fibers of the deltoid muscle). The medial fibers abduct the humerus, raising the humerus away from the side of the body.

The supraspinatus is one of the rotator cuff muscles and is activated by seated lateral raises. It begins near the cervical vertebrae, and attaches on the head of the humerus. Like the medial deltoid, the supraspinatus abducts the humerus. It also keeps the head of the humerus in the shoulder joint. The shoulder has been designed for mobility rather than stability. As a result, lifting huge weights has a greater potential to induce injury to the shoulder than other, more stable joints. This does not mean that you should not train the shoulders with decent loads, but the super-heavy stuff should be reserved for squats and deadlifts. Seated dumbbell side laterals provide superb stimulation for the medial fibers of the deltoids, without the need for hoisting super-heavy weights or risking injury to the rotator cuff muscles.

Dumbbell Side Lateral Raises

1. Place a short-backed 90º bench in front of a mirror. Sit on the bench and take a dumbbell in each hand. Turn your palms toward the side of your thighs.

2. Your elbows should be just short of straight, but your elbow joint angle should not change throughout the range of motion. Lean slightly forward, but look up so that you can see your arms in the mirror.

3. Slowly and simultaneously raise both dumbbells from a position that is beside your thighs, and continue lifting until the hands are just slightly above shoulder level. This is abduction of the arms. Both arms should work at the same time, and you should be able to draw a line that runs from one arm, through the shoulders, to the other arm. Your palms should be facing the floor as you are lifting the weight upward.

4. Continue to raise the dumbbells out to the side of the body until they are at shoulder level, so your arms are parallel to the floor. Rising higher than this will stimulate the trapezius, but it will not help develop the deltoid muscles any further.

5. As the top position is approached, begin to pronate the hands until the knuckle of the little finger is at about a 45º angle, relative to the ceiling. Hold the top position briefly.

6. Slowly return your arms to the sides by retracing your steps. This means that you will turn your palms back to a position that is facing the floor, then lower your arms toward your thighs.

6. Do not pause at the bottom, but immediately begin the lift upward. This will keep the fibers in the medial deltoid firing throughout the set. After you have completed 12-15 full reps, you can rest 60-90 seconds before starting your next set.

Many people sit too vertically during this exercise. To maximize activation of the medial fibers of the deltoid, remember to bend forward just a little. However, don’t bend your torso too far forward, otherwise the rear deltoids will get the load.

The next important point about this exercise is to make sure that you rotate at your shoulder (not just at the wrist), to make the knuckle of the little finger move upward as you approach the top of the lift. It is also important that you do the exercise strictly, without jerky movements. It is not necessary to worry too much about lifting superhuman weight. On the other hand, you cannot expect good results if you are lifting pencil weight, either.

The road to shoulder greatness is not easy, and you will have to push yourself if you want to be outstanding. Fully sliced shoulders are within your reach – if you want them badly enough. When the Average Joe wants to quit, you need to do 2 more reps. If you are careful in your exercise form and diligent in your training, over the next few months you should see new thickness and contours emerging from the recesses of your short-sleeve shirts.

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References:

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Minning S, Eliot CA, Uhl TL & Malone TR 2007. EMG analysis of shoulder muscle fatigue during resisted isometric shoulder elevation. J Electromyogr Kinesiol, 17, 153-159.

Moore KL and AF Dalley. Clinically oriented Anatomy, Fourth Edition. Baltimore, Lippincott Williams & Williams, Kelly, PJ Editor, 1992, pp. 690-698.

Reinold MM, Macrina LC, Wilk KE, Fleisig GS, Dun S, Barrentine SW, Ellerbusch MT & Andrews JR 2007. Electromyographic analysis of the supraspinatus and deltoid muscles during 3 common rehabilitation exercises. J Athl Train, 42, 464-469.

Yasojima T, Kizuka T, Noguchi H, Shiraki H, Mukai N & Miyanaga Y 2008. Differences in EMG activity in scapular plane abduction under variable arm positions and loading conditions. Med Sci Sports Exerc, 40, 716-72.

Uhl TL, Muir TA & Lawson L 2010. Electromyographical Assessment of Passive, Active Assistive, and Active Shoulder Rehabilitation Exercises. PMR, 2, 132-141.