Carrying the World on Your Shoulders
by: Jonathon Fass
WARNING: for those of you who are regular readers of Mind & Muscle, this article may very well leave you feeling unsettled, maybe even a bit confused. There will be NO discussion of leptin and JAK pathway signaling, not a hint of androgen receptor binding, and not even the slightest mention of AMPk inhibition of acetyl-CoA carboxylase. For those of you brave enough to continue, you have been warned.
This article will discuss the forgotten child of bodybuilding: the shunned sciences of arthrokinematics and biomechanics. These are vital knowledge for anyone who’s ever lifted a weight, thrown a ball, or gotten out of a chair. Kinesiology nevertheless cowers in the shadows of the more glamorous and exciting worlds of endocrinology and bioenergetics. Yet without a complete understanding of the principles of human movement and joint health, chronic and misunderstood exercise can, at best, limit your results and reduce progress. At worst, it can end a career and permanently disable.
A complete discussion of biomechanics is far beyond the capabilities of just one article; therefore, this discussion will focus only on the shoulder (the glenohumeral joint specifically). Of the four joints (the acromioclavicular joint, sternoclavicular joint, and scapulaothoracic joint) that combine to produce complete movement of the humerus, the shoulder complex, and proper scapulohumeral rhythm; the glenohumeral joint is one of the most important, and most often injured joints in the body.
The glenohumeral joint is comprised of the convex head of the humerus and the concave glenoid fossa, found on the anterior lateral border of the scapula (1, 2). The humeral head is positioned medially and superiorly at an approximate angle of 135° in respect to the humeral shaft. It is rotated posteriorly 30°, causing a retroversion which orients the humeral head within the scapular plane, improving congruency and articulation with the glenoid fossa (1). The glenoid fossa itself is positioned in an upward rotation of approximately 5° in anatomical position, and is approximately 1/3rd the size of the humeral head (3).
The glenohumeral joint is covered by a dense network of connective tissue and structures in order to achieve stability. The joint itself is surrounded by a synovial capsule that attaches along the outer edge of the glenoid fossa and extends to the anatomic neck of the humerus (1). This synovial membrane also engulfs the tendon of the long head of the biceps as it extends through this capsule, passing from its origin on the supraglenoid tubercle through the intertubercular sulcus.
Four glenohumeral capsular ligaments found on the anterior and inferior walls of the capsule reduce extreme motion of the humerus. The superior glenohumeral ligament becomes taught and restricts further movement at the point of full adduction, as well as preventing posterior and inferior translation of the humeral head. The middle glenohumeral ligament prevents anterior translation and extreme external rotation. The inferior glenohumeral ligament is composed of an anterior band, a posterior band, and connecting axillary pouch. It inhibits excessive abduction as well as external rotation (anterior band) and internal rotation (posterior band).
Finally, the coracohumeral ligament prevents extreme range of motion in external rotation, flexion, extension, and inferior humeral translation (1, 17). Injury to the capsule and/or the capsular ligaments can result in deficiencies of movement and stability (17).
The glenoid labrum (a ring of fibrocartilage that surrounds the rim of the glenoid fossa), significantly increases the contact area and hence congruency and stability of the humeral head by up to 75% and 20%, respectively; more than would be available in its absence (2,3,7). The labrum surrounds the long head of the biceps by means of a partial extension of the labrum, acting as an aspect of its origin, and directly involving the biceps brachii in support of the shoulder (1).
Eight bursa sacs can be found in the glenohumeral joint, found in regions of high frictional forces (8,9,10). There are two important bursa: the subacromial bursa (which serves to protect the supraspinatus from interacting directly with the underside of the acromion), and the subdeltoid bursa (which protects the deltoid from experiencing frictional irritation from interaction with either the supraspinatus tendon and/or the humeral head) (1,9,12). Irritation and subsequent inflammation of the bursae can be painful and reduce normal range of motion (9).
Lastly, the coracoacromial arch is formed by the coracoacromial ligament and its attachment to the acromion process which is found superior, anteriorly and lateraly to the glenoid fossa. Functioning as the ‘roof’ of the glenohumeral joint, the coracoacromial arch forms the superior border of the subacromial space, in which the supraspinatus muscle belly and tendon, biceps tendon, subacromial bursa, and portion of the superior capsule can be found (1). This is an especially prominent site for injuries resulting from improper lifting form, techniques and workout programming, as the supraspinatus itself can become compressed, impinged, or even damaged and ruptured from chronic misuse (1,2,3,5,12,14).
In addition to the biceps, the posterior deltoid also plays a role in humeral stabilization and functions as a distal stabilizer (1); most importantly, however, are the four muscles of the rotator cuff in establishing humeral stability: the supraspinatus, infraspinatus, teres minor, and subscapularis. The supraspinatus compresses the humeral head directly into the glenoid fossa, as well as in assisting in adduction as well as extension of the arm. The infraspinatus and teres minor both produce an inferior translational force on the humeral head, as well as causing external rotation of the arm. Finally, the subscapularis medially rotates the humerus, as well as adding to the inferiorly-directed force caused by the infraspinatus and teres minor (1,2,3). The proper functioning and adequate strengthening of the rotator cuff muscles is imperative for the health and pain-free longevity of the glenohumeral joint, and these muscles are responsible for the majority of stability found at the shoulder (1,3,4,5).
The glenohumeral joint is the classic example of a ball and socket joint, which allows the shoulder a wide array of movement possibilities and motion in all 3 degrees of freedom. The shoulder complex is capable of 180° of flexion, 60° of extension, and 180° of abduction in a healthy individual (11), of which the glenohumeral joint contributes 2/3rds of the movement in both flexion and abduction (1). The glenohumeral joint is also capable of producing 70° of medial rotation, and 90° of lateral rotation.
During abduction, the humeral head will experience a ‘roll-and-slide’ arthrokinematic movement along longitudinal diameter of the humeral head in order to maintain contact with the surface of the smaller glenoid fossa (1). As the humeral head rotates upwardly (the ‘roll’), it will simultaneously translate inferiorly (‘slide’). Without this mechanism, the abduction of the humeral head would cause an impingement against the coracoachromial arch, impeding movement and damaging tissue. Weakness of the rotator cuff muscles and/or poor neural activation of these muscles can disrupt proper kinematics and result in pain and injury (3,4,5).
Without the rotator cuff available for stabilizing the humeral head medially and inferiorly, the deltoid would pull the humeral head upwards towards the subacromial space. In addition, any narrowing of the subacromial space, either through muscle imbalance leading to superior migration of the humerus, bone spurs, osteophytes, thickening/inflammation of the subacromial bursa, or a genetically formed irregular shaping of the acromion process can all impact normal biomechanics and lead to injury (3,5,15).
Health and Exercise
At this point, you should have come to a number of realizations:
- The shoulder (and the glenohumeral joint itself), is a complicated and extremely versatile joint.
- The shoulder can also be as brittle as a stale piece of toast if you do the wrong things to it.
- I like to use fancy anatomy terminology to make myself sound smart.
Just open your eyes, and you can see that most people have poor posture and exhibit an anterior or superior translation of their glenohumeral joint, which result from weakness of the scapular retractors (middle Trapezius, lower Trapezius, Rhomboid major & Rhomboid minor) and rotator cuff muscles. In fact, posture has been directly shown to be a contributing factor to increasing the risk of shoulder pathology (16). Bodybuilders in particular have been shown to have poor shoulder ROM and shoulder positioning when compared to normal populations (13). Too much pressing and not enough pulling in the gym, worrying too much about the beach and not enough about balance may be partially to blame, along with a lack of proper flexibility training (14). Both are easily corrected, but rarely addressed by both lifters and personal trainers alike.
Common exercises such as the lat pulldown and bench press (both barbell and dumbbell) should both be performed with a slight anterior positioning of the elbows of approximately 30° horizontally adducted, and excessively wide hand spacing (>1.5x shoulder width) should be avoided (18). Exercises that cause internal rotation during abduction, such as the upright row, should also be avoided. This movement combination will cause the greater tubercle of the humerus to come into contact with the supraspinatus and press it against the subacromial bursa and coracoacromial arch (18). Finally, extreme ranges of motion, as well as behind-the-neck techniques should also be avoided (unless in the case of a sport-specific need, which should be evaluated by and performed under the care of a qualified coach or sports medicine practitioner), due to the excessive pressures that these techniques will place on the capsule and ligaments, contributing to joint laxity and instability (18).
If you have been experiencing any form of shoulder pain, the first step is to see a qualified professional to rule out a serious shoulder issue. However, even if you have never felt the slightest twinge of discomfort in your shoulders, the addition of the following exercises, along with a complete upper body flexibility routine within an otherwise properly balanced program can mean the difference between pain-free and painful:
- Reverse Shrugs: Assume the locked-out, peak position of a chest dip. While maintaining straight arms, elevate and depress the shoulders in a shrug motion. Prime Movers: lower Trapezius, Latissimus Dorsi, Serratus Anterior.
- Wall ‘W’s’: While standing with your back against a wall, press the dorsal surfaces of your hands and elbows against the wall, with your arms elevated above your head. Slide your arms downwards, as in a lat-pull motion, while keeping the back of the hands and elbows in contact with the wall, then return to the start position. Prime movers: mid & lower Trapezius, Latissimus Dorsi, Rhomboids, middle & posterior Deltoids.
- Internal Rotations: With your arm fixed to your side and elbow flexed to 90°, rotate your arm medially, using a pulley for resistance. Prime Movers: Subscapularis, anterior Deltoid, Pectoralis Major, Latissimus Dorsi, Teres Major.
- External Rotations: Starting with your arm from the internally rotated position, arm fixed to your side and elbow bent 90°, rotate your arm laterally until it is slightly past neutral in the sagital plane. Prime Movers: Infraspinatus, Teres Minor, Posterior Deltoid.
- Bent-over Angled Shoulder Raises: Bend at the waist approximately 30-45°, holding a bar, using a snatch grip. Without standing straight, raise the hands up to eye/head level. Prime Movers: Deltoids, Infraspinatus, Teres Minor, Mid Trapezius, Rhomboids, Latissimus Dorsi, Erector Spinae.
1. Neumann, D. Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Mosby, Inc. 2002.
2. Hamill, J., and Knutzen, K. Biomechanical Basis of Human Movement, 3rd Edition. Lippincott Williams & Wilkins. 2003.
3. Ronai, P. Exercise Modifications and Strategies to Enhance Shoulder Function, Strength and Cond J., vol. 27, no. 4. (2005), 36-45.
4. Hess, S., Richardson, C., Darnell, R., Friis, P., Lisle, D., and Myers, P. Timing of Rotator Cuff Activation During Shoulder External Rotation in Throwers With and Without Symptoms of Pain, J. Orthop. Sports Phys. Ther., vol. 35, no. 12 (2005), 812-820.
5. Ludewig, P., Cook, T., Alterations in Shoulder Kinematics and Associated Muscle Activity in People With Symptoms of Shoulder Impingement, Phys. Ther., vol. 80, no. 3 (2000)
6. Harryman, D., Sidles, J., Clark, J., McQuade, K., Gibb, T., and Matsen, F.
Translation of the Humeral Head on the Glenoid with Passive Glenohumeral Motion, J. Bone and Joint Surgery, vol. 72, no. 9 (1990) 1334-1343.
7. Soslowsky, L., Flatow, E., Bigliani, L., and Mow, V. Articular Geometry of the
Glenohumeral Joint. Clin. Orthop. Relat. Res., Vol. 285 (1992) 181-190.
8. Halder, A., Itoi, E., and Nan-Kai, A. Anatomy and Biomechanics of the Shoulder,
Orthop. Clin. N. Amer., vol. 31, no. 2 (2000) 151-176.
9. van Holsbeeck, M., Strouse, P., Sonography of the Shoulder: Evaluation of the
Subacromial-Subdeltoid Bursa, Am. J. Roentgen., vol. 160 (1993) 561-564.
10. Nottage, W., Arthroscopic anatomy of the glenohumeral joint and subacromial bursa.
Orthop. Clin. North Am., vol. 24, no. 1 (1993) 27-32.
11. Norkin, C., White, Joyce, Measurement of Joint Motion: A Guide to Goniometry, 3rd
Edition. F.A. Davis Company. 2003.
12. Roy, A., Dahan, T., Manon, B., and Dahan, B. Rotator Cuff Disease. www.Emedicine.com
13. Barlow, J., Benjamin, B., Birt, P., and Hughes, C. Shoulder Strength and Range-of-Motion Characteristics in Bodybuilders. J. Strength Cond. Res., vol. 16, no. 3 (2002) 367-372.
14. Tyler, T., Nicholas, S., Roy, T., and Gleim, G., Quantification of Posterior Capsule
Tightness and Motion Loss in Patients with Shoulder Impingement, Am. J. Sports
Med., vol. 28 (2000) 668-673.
15. Jobe, C., Superior Glenoid Impingement: Current Concepts., Clin. Orth. Rel. Res.,
vol. 330 (1996) 98-107.
16. Brossmann, J., Preidler, K., Pedowitz, R., White, L., Trudell, D., and Resnick, D.
Shoulder Impingement Syndrome: Influence of Shoulder Position on Rotator Cuff
Impingement–an Anatomic Study, Am. J. Roentgen., vol. 167 (1996) 1511-1515.
17. O’Connell, P., Nuber, G., Mileski, R., and Lautenschlager, E., The Contribution of the Glenohumeral Ligaments to Anterior Stability of the Shoulder Joint, Am. J. Sports Med., vol. 18, no. 6 (1990) 579-584.
18. Durall, C., Manske, R., Davies, G., Avoiding Shoulder Injury from Resistance Training, Strength and Cond J., vol. 23, no. 5. (2001), 10-18.