Any exercise, especially one that involves resistance, can lead to an injury if you perform it improperly or if is biomechanically incorrect for what you want to do. The shrug, as simple as it may seem, falls into the category of movements that many people do inorrectly.
The shrug is intended primarily to develop the size and strength of your trapezius muscles. There is another muscle that lies underneath the trapezius that comes into play when you perform this exercise: the levator scapulae, which elevates the scapula (shoulder blade).
Your traps have three anatomic and four kinesiologic components apiece, one set on each side. Anatomically, the trapezius is a large muscle that's divided into upper, middle and lower portions. As a unit the traps are the kite shaped muscles that run across the upper and middle back. They are easy to spot on a bodybuilder who's in contest shape.
The trapezius originates on the vertebrae of the entire thoracic spine (midback and cervical spine (neck), and it inserts on the shoulder blade on a bony prominence that follows along the shoulder, the outer third of the clavicle (collar bone) and into the base of the skull.
This discussion concerns the portion of the muscle that crosses over the acromiclavicular (AC) joint, which is located at the junction of the collar bone and the front of the shoulder blade.
The upper trapezius elevates the scapula, as in a shrug, and upwardly rotates it, as in an overhead press. The middle trapezius primarily retracts the scapula - that is, pulls it together, as in a rowing motion. The lower trapezius primarily rotates the scapula inward, as well as assisting in retraction. The upper trapezius also assists somewhat in retraction.
In terms of the kinesiology, or the way the muscle moves, the trapezius is said to have four components because the upper trapezius is further divided into two portions where the angle of the fibers change. When you do shrugs, however, both portions of the upper traps perform the same action. The traps can assist in stabilizing the AC joint because it surrounds the superior (top) surface of the joint.
There are a number of different ways to perform shrugs that have come into favor at some time or other. Some variations can cause shoulder pain or aggravate an existing problem. At the very least they may be biomechanically incorrect for what you're trying to do.
This discussion addresses the common variety shrug in which you shrug your shoulders, or elevate them, and then roll them back and down to perform a complete rep.
The upper trapezius does the initial work of shrugging. According to longtime training "wisdom," you roll the shoulders back after that to train the middle and lower traps, since these are the parts that pull the shoulder blades back. Once again a little truth and a lot of poorly planned effort can go a long way toward leaving you susceptible to injury.
Let's look at this shrugging and rolling idea a little more clearly. The effect of gravity on the weight provides the vertical resistance to work the upper trapezius. Your upper traps contract, and the resistance is constant due to the constant pull of gravity. When you draw back your shoulders, the effect of gravity is still vertical, but because you are rolling your shoulders back, you're now creating an opposing contraction on a more horizontal plane. In other words, the resistance for the second part of the movement, rolling your shoulders, is only minimally effective. If you want to work your middle and lower traps with the maximum resistance, the movement must come from somewhere in front of your body, as in cable rows or barbell rows.
It makes very little sense biomechanically to bother with the "rolling back" part of the shrug. In the very best case it is simply an inefficient effort. With respect to potential for injury - and what you can do to prevent injuries and keep training - the rolled back shrug puts a lot of stress on the AC joint.
If you have a previous injury in that area, the joint is likely less stable and more mobile. Retracting, or rolling back your shoulders, tends to "open" the joint, thus reinforcing its instability. The result can be pain when you do shrugs or, even worse, when you do other exercises, which makes it difficult to identify what's causing the pain, even for an experienced clinical sleuth.
The bottom line is simple: If you know that you had some form of AC joint separation also known as shoulder separation, don't roll your shoulders back when you do shrugs. If you don't know for sure what happened to you and you experience pain on top of your shoulder, or if you have noticed that the top of one shoulder seems more prominent than the other, you may very well have separated an AC joint at some time. Another possible sign is if you feel pain on top of your shoulder when you perform dips.
These are only a couple of the possible indicators of this problem, however. Don't attempt to diagnose yourself.
You can still do shrugs if yo8u have had some form of shoulder separation in the past; in fact, you can use them to help stabilize the AC joint. Just perform shrugs with a straight up-and-down movement, without rolling your shoulders. Also, do not relax in the bottom position of the movement. Relaxing at the bottom of a shrug places a lot of traction - that is, it has a stretching effect - on the entire shoulder. It aggravates the rotator cuff, as well as the unstable AC.
Do use as full a range of motion as possible - but keep the bottom position under complete control. Strengthening the upper trapezius will help keep the AC joint more approximated (closer) and will make it more stable over time. It will not, however, restore the joint to its original strength and stability.
All the above applies to dumbbell shrugs as well. Because of the greater freedom of movement when using dumbbells, many lifters tend to "roll" their dumbbell shrugs.
The shrug can lend itself to a great deal of weight. Increase your poundages progressively, or you could suffer tendinitis over the top of your shoulder blades (spine of the scapula) at the insertion of the trapezius. If this happens, reduce the weight substantially or take a brief layoff. Place an ice pack over the sore area for 20 minutes twice each day for one week. Never use heat, as this will increase the inflammation. Start doing shrugs again with light weight and gradually increase the poundage.
The shrug is not the only exercise in which the retraction of the scapula can aggravate the AC joi9nt. The pec deck, for example, causes a similar effect. I'll discuss the other movements that can lead to AC problems in a future article.
Enjoy Your Lifting!