Columbia Advanced Chiropractic Blog, Body at Work

Shoulder Biomechanics and Impingement Syndrome 101

The first Body at Work blog topic is one that will hopefully pique your interest.  Many of us go to the gym to exercise, and this is a good thing.  However, all too many of us perform exercises that are dangerous.  The reasons for this are plentiful, but what can we do to ensure that we know what we are doing?  Also, if we use a fitness professional, are we sure that the individual’s training is at a high level?  For this blog, I’ll go over one common gym movement that creates significant damage to your body, over time.  

For some background, our shoulders give up stability for lots of mobility (in comparison with the hip joint).  Due to this, we have to be quite careful with how we exercise/train our shoulders.  The rotator cuff, which is a combination of four muscles, functions as dynamic stabilization for the shoulder.  This means its function is to keep the shoulder in check while other muscles work to move it.  Although the rotator cuff musculature needs to be healthy and strong, we still have to address this region carefully.

We have what we are born with.  In regards to the shoulder, this means some of us have an advantage and some a disadvantage when it comes to shoulder biomechanics.  This comes into play when we discuss injury potential with at least one region of the shoulder.  A big consideration with shoulder function involves the ‘type’ of Acromion process you have.  The acromion process is a piece of bone that is part of the scapula bone (that triangular bone in your upper back). The acromion comes up and around the top of your shoulder and articulates with the lateral portion of the clavicle to form the acromioclavicular joint.   This joint is one of the three joints of the shoulder (the other two are the sternoclavicular joint…where the sternum meets the medial clavicle, and the glenohumeral joint…where the head of the humerus bone attaches to the shoulder region).

There are three primary shapes of the acromion process.  Type I is flat, Type II is curved, and Type III is hooked, or beaked.  The shape of the acromion will largely determine the health of your shoulder, especially if you perform exercises that create impingement.

Although there are several types of impingement, the main one we deal with in the shoulder is the impingement of the supraspinatus muscle/tendon (one of the four rotator cuff muscles) as it comes under the acromion process.  Under the acromion process, we also have a couple of bursa sacs.  We don’t even know these are present until we have pain, ouch!

Now back to those acromion types.  If you’re lucky enough to have a Type I acromion, you have a reduced likelihood of impingement.  With a Type II, the acromion, with certain shoulder movements, is more likely to impinge upon the supraspinatus and two bursa sacs.  With a Type III, it is much more likely to create damage.  This doesn’t even take into consideration the greater likelihood of arthritic changes (spurs) in the region with Type II and III acromion processes.

Now, let’s take a look at what we do in the gym.  The movement of shoulder abduction (straight out to the side), which we call movement in the frontal (coronal) plane, will create pinching, or impingement of the structures under the acromion process.  To demonstrate this, stand up, put your arm at your side with the palm against your body, and raise your arm straight up to the side.  When you get your arm a little above your head, you’ll notice that it’s hard to get the arm to go all the way up unless you either rotate the arm, or move it in front of your body a little to get it to go all the way up.  This demonstrates impingement as you are compressing structures and doing so blocks your shoulder’s ability to go all the way up.  Now imagine repeatedly performing this exercise with weight…can you imagine the amount of impingement that can be caused by doing so?  The bottom line is that exercises that bring the arm up at the side (above 60 degrees) create impingement, especially with a Type II or Type III acromion, and these exercises can quickly lead to serious shoulder injury.

So, now loaded with this infomation as a basis, what are common exercises performed in the coronal plane and what can we change, or replace them with, to avoid creating shoulder damage?  Is it even necessary to move the shoulder in the coronal plane when we exercise?  Do certain shoulder exercises compromise other structures in the shoulder?  So, let the discussion begin.

For reference, below is a picture of the acromion process types, so that you can get a good idea of the anatomy of the region and visualize how the different shapes of the acromion processes can impinge upon the structures below them.

Acromion processes...three types...

Three types of acromion processes: Magee D. Orthopedic Physical Assessment. 3rd ed. Philadelphia: W.B. Saunders; 1997.


  1. Hi there, I have a Type II acromion and thus suffer some irritated bursas and slightly impingement. This is affecting my weight lifting routines and I was wondering if you have another resource which actually shows the exercises that we can perform to eliminate the pain and irritation and avoid the impingement. I’m hoping to avoid surgery in the future.

    Kindest Regards,

    Comment by Peter Hatzidimitriou — August 12, 2013 @ 11:17 PM

  2. Peter,

    This is not so easily answered but I’ll try to help. The impingement caused by a Type II acromion can be reduced by avoiding movement in the coronal/frontal plane…this means bringing your arm up to your side…such as with a side deltoid raise or upright row…these exercises will destroy any shoulder! If you move in what is called the scapular plane (about 20-30 degrees anterior to the coronal plane), you reduce the impingement by moving the supraspinatus muscle out of the way of the acromion.

    You might also want to find an ART provider or someone who is well-trained in dealing with rotator cuff issues. Although the acromion cannot be changed without surgical means, you can do a lot with conservative measures to avoid surgery.

    Another thing you should consider is working on scapular stability, to avoid excessive movement in the glenohumeral joint (shoulder) that will lead to more irritation. There is a group of exercises called the Buchberger 12 (look online). Most (not all) of those exercises are good…it provides a good guide to start with.

    By all means, though, no more coronal plane movements…period…they will create problems…regardless of what type of acromion you have…

    Take care,

    Dr. M

    Comment by Dr. M — August 13, 2013 @ 6:39 AM

  3. Thanks so much for the reply Dr. M…I am having more biceps tendon pain then actual rotator cuff pain these days. I’m still trying to get my ROM improved and the tendon to settle down…its a constant struggle but I feel like I’m making slow progress.


    Comment by Peter — November 27, 2013 @ 9:11 AM

  4. As long as you are making progress, this is what counts. You might want to find someone certified in RockTape who can help support your healing tissues. Don’t underestimate the power of functional taping…it really can yield great benefits. Good luck and keep up the good work!

    Dr. M

    Comment by Dr. M — December 19, 2013 @ 12:19 AM

  5. I am a type 3 acromion and have developed a slight tear in my rotator cuff. Is surgery they only way to prevent it from getting worse.

    Comment by Tim — July 24, 2014 @ 7:02 PM

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