The shoulder is the most complex joint in the body. It has a small ball and socket joint that’s very unstable and it’s literally held in place by muscles and tendons. Thus, it’s not surprising that the shoulder is vulnerable to injury. On the other hand, shoulder instability provides a mechanism for enormous movement possibilities so that we can freely manipulate our environment. Shoulder injury can be avoided, however, if the soft tissue structures that support the joint are strong and not overly stretched (i.e., torn).
Form and Function
The functions at the shoulder include rotation, flexion and extension. Depending on which fibers and muscles are active, the shoulder is capable of medial and lateral rotation, flexion (bringing the arm forward) and extension (bringing the arm backward) of the humerus bone.
Deltoid muscle. The deltoid is a thick, powerful, muscle that caps the other muscles of the shoulder joint, and covers the bony connections that make up the shoulder. The deltoid is thought of as three muscles each having a different head. Although they are not truly separate heads, the deltoid originates from three regions on the bony portions of the shoulder and has several functions.
The anterior fibers begin along the lateral part of the clavicle (collarbone). The posterior fibers attach along the spine of the scapula (shoulder blade). The medial fibers begin in regions between the previous two sites on the acromion of the scapula. All fibers from the deltoid converge on the anterior and upper portion of the humerus bone called the deltoid tuberosity. This is a bumpy part almost halfway between the shoulder and elbow on the lateral aspect of the humerus bone of the upper arm.
Rotator Cuff Muscles
Four scapular muscles (subscapularis, supraspinatus, infraspinatus and teres minor) form the rotator cuff muscles and fulfill many of the movements associated with the shoulder. All but the supraspinatus are rotators of the humerus at the shoulder.
Infraspinatus and Teres Minor. The infraspinatus muscle fills most of the infraspinatus fossa and attaches between this fossa and the greater tubercle of the humerus. Its function is to rotate the humerus laterally. The teres minor muscle attaches between the superior (upper) part of the lateral border of the scapula and the greater tubercle of the humerus. It laterally rotates the humerus and helps stabilize the shoulder joint.
Supraspinatus. The supraspinatus is a rounded muscle that lies in a hollowed out area on the top part of the posterior side of the scapula. It begins near the medial side of the scapula and runs over to the superior part of the head of the humerus. It lies deep to the trapezius muscle and part of it is also deep to the coracromial arch (strong ligaments connecting the coracoid process of the scapula to the acromion – the end part of the spine of the scapula. The tendon of the supraspinatus is covered by the deltoid. Along with the lateral fibers of the deltoid, the supraspinatus acts to abduct the humerus (raise the arm to the side with a straight elbow). It’s the only muscle of the rotator cuff that doesn’t have a rotational function.
Subscapularis. Unlike the other muscles of the rotator cuff, this muscle lives exclusively on the front (anterior) side of the scapula. It crosses the anterior part of the shoulder joint and inserts on the lesser tubercle of the humerus. This muscle is a strong medial rotator of the humerus.
Potential For Injury
If you lift your arms to a position over your head, the head of your humerus bone moves laterally as it is forced inferiorly. This tends to stretch the supraspinatus muscle. Too much stretch, however, can cause small tears in the muscle and its tendinous attachments. This results in shoulder pain, swelling and frequently tendinitis. The supraspinatus will develop microtears that may lead to more substantial tears and swelling in the soft tissue. Thus, heavy or explosive lifts (or even fast descents) may result in the muscle becoming damaged. It’s not just direct shoulder exercises that could damage the rotator cuff and other shoulder muscles; just about any upper body exercise has some potential for such injury. The solution is to make sure all aspects of the shoulder and rotator cuff are strong.
During everyday movement, the rotator cuff muscles, especially the supraspinatus, are susceptible to repeated microtramuas and small microscopic tears. Usually, the source of micro-damage is impingement (pinching) against the coracromial arch when the shoulder joint is abducted or flexed.
Because there’s not much space in the area below the acromion arch, the subacromial bursa is critical to smooth and pain free shoulder movements. Excessive abduction of the arm at the shoulder joint can cause inflammation of the bursa, or bursitis. Bursitis of the subacromial bursae occurs because it becomes inflamed after being pinched and compressed during sliding movements of the supraspinatus and other tendons across it.
Alternating Front and Lateral Dumbbell Raise
Improvements of the deltoid and rotator cuff muscles can be achieved by the following combination of two dumbbell exercises. The first part is a lateral raise from the side of your thighs to shoulder level. The second is to arch the dumbbell from the side to finish at about eye level in front of your body.
- First, warm up the shoulder with some stretching, then a set or two (e.g., 15-20 repetitions) of light dumbbell presses. Start with elbows pointed to the floor with arms adjacent on the corresponding lateral sides of the rib cage. Palms should be pronated (facing toward the rear). Press the dumbbells upward, but after a couple of inches as you reach eye level, begin to press the dumbbells so they’re in a line in front of your face rather than directly over your head. The dumbbells should come together but not quite touch at the top of the movement. This is like an “A,” with a wider position at the start and finishing at the apex. Continue pressing upward; at the top of the movement your elbows should be bent and pointing to the sides at about ear level. Don’t straighten your elbows.
- Slowly lower the weight to the starting position and reverse the movements by bringing your elbows back to the lateral side of the rib cage. Now you’re ready for the real thing. Begin with a dumbbell in each hand and your arms hanging straight beside your torso. Each dumbbell should be turned so your palm faces toward the side of your thigh. Your elbows should be just short of straight, but the elbow joint angle should not change throughout the range of motion. Your feet should be wide enough to provide a good base of support.
- Lean slightly forward, but make sure your lower back and gluteal muscles are tight and your knees are slightly bent to reduce unnecessary lower back movement or strain. Keep elbows slightly bent and raise the dumbbells to a position slightly above shoulder level.
- Do not lift the dumbbell higher than parallel to the floor. The deltoid does not contract any further once you reach the parallel position, but other muscles (e.g., serratus anterior, trapezius) do contract to allow you to rotate the scapula to bring the arm above a position parallel to the floor. Lifting the weight higher puts more stretch/stress on the supraspinatus muscle without benefit.
- As the top position is approached, rotate each shoulder so the knuckles of the little fingers are pointing upward. This “twist” will be produced by a medial rotation at the shoulder joint and not at the wrist. Hold this top position for a count of two to isometrically contract the deltoid. This extra rotation will also bring the anterolateral region of the deltoid into play (fibers between the lateral and anterior regions) and thereby thicken the tie-in between these two regions of the deltoid).
- Now begin the descent with the weight as you slowly rotate your shoulders laterally. This will result in a slight supination of your hands. Then return the dumbbells slowly to the starting position with the dumbbells on the lateral side of your thighs and your hands pronated (palm facing away from your face toward the rear).
- From this position, start upward again, but this time move the dumbbells in front of your body instead of keeping them at the side. Your elbows should remain slightly bent to avert unnecessary shearing forces, but prevent your elbow angle from changing throughout the movement.
- Raise the dumbbells in an arc from the starting lateral position to finish at, or slightly below, eye level. As you raise your arms and dumbbells, rotate your shoulders so your little finger is facing upward, just as you did for the lateral raise. This time though, you’ll feel the muscle contraction more anteriorly in the shoulder. After you reach the top, begin the descent back to a position with the dumbbells on either side of the lateral aspects of your thighs.
- Repeat the sequence without resting until the set is complete (e.g., 8-10 lateral raises alternated with 8-10 front raises). After each set, swing your arms back and forth to attempt to get as much blood to the shoulders as possible.
Position, Speed and Resistance
Arm and elbow position. Elbows should point away from your torso throughout. This position favors activation of the medial fibers of the deltoid and simultaneously stretches the anterior fibers of the deltoid to improve mechanical activation. Most of the safe and effective work for the rotator cuff and deltoid is complete by the time the upper arms have become parallel to the floor, so it’s never necessary or desirable to raise your arms much beyond this point. Keep the anterior deltoids under constant tension; don’t relax with your arms hanging at your sides between repetitions.
Wrist position. Lock the wrist so all the rotation movement occurs at the shoulder joint. If you allow the wrists to rotate, this will drastically decrease the effectiveness of the exercise.
Velocity of movement. Avoid jerking or explosively lifting the dumbbells in a lateral raise because this would almost certainly result in tears of the supraspinatus. Don’t rotate the shoulder in a jerky or ballistic manner, especially when you’re medially rotating the arm at the shoulder joint. This would likely result in microtears in the subscapularis muscle followed by significant shoulder pain.
Resistance. Extremely heavy weights can cause further joint instability and increase injury risk, particularly if exercises are done quickly or under extreme ranges of motion. You still must be willing to work hard and intensely; however, you must also work intelligently. Warming up a joint with light weight is important.
Remember, the shoulder joint is literally held together by its muscle attachments, not other bones. Thus, stronger shoulder muscles mean greater shoulder stability and reduced risks for injury.
Basmajian JV. Recent advances in the functional anatomy of the upper limb. Am J Phys Med, 48:165, 1969.
Basmajian JV and CJ Deluca. Muscles Alive. 5th Edition. Baltimore, Williams and Wilkins, pp. 220-224, 1985.
Clemente CD. Anatomy, A regional atlas of the human body. Second edition, Baltimore, Urban & Schwarzenberg Pub. Co. p.33-75, 1981.
Codine P, Bernard PL, et al. Influence of sports discipline on shoulder rotator cuff balance. Medicine & Science in Sports & Exercise, 29(11):1400-5, 1997.
Doody S G, L Freedman and JC Waterland. Shoulder movements during abduction in the scapular plane. Arch Phys Med Rehabil, 51:595, 1970.
Freedman L and RR Munro. Abduction of the arm in the scapular plane. Scapular andglenohumeral movements. A Roentgenographic study. J Bone Joint Surg, 48A:1053, 1966.
Kestens B, Hoogmartens M. The hung up shoulder: anterior subluxation locking in abduction. Acta Orthopaedica Belgica, 63(3):165-9, 1997.
Kuechle DK. Newman SR et al. Shoulder muscle moment arms during horizontal flexion and elevation. Journal of Shoulder & Elbow Surgery, 6(5):429-39, 1997.
Moore KL and AM Agur. Essential Clinically Anatomy, Williams and Wilkins, 1995.
Netter FH. Atlas of Human Anatomy, 2nd Edition, Frank H. Netter, Ciba-Geigy, 1997.
Nelson CL. Athletic injuries of the shoulder. Cleveland Clin Quart, 40:27, 1973.
Penny JN and PP Welsh. Shoulder impingement syndromes in athletes and their surgical management. Am J Sports Med, 9:11, 1981.
Rasch PJ. Kinesiology and Applied Anatomy. Seventh edition. Philadelphia, London. Lea & Febiger, pp. 117-135, 1989.
Saha AK. Dynamic stability of the glenohumeral joint. Acta Orthop Scand, 42:491, 1971.