14 Dec Anatomical Variation In The Shoulder (What It Could Mean For You)

Trouble with overhead motion? Is the overhead press uncomfortable or painful for you? There may be a legitimate reason why.

I’ve come to believe that the overhead press is one of the most important and valuable exercises for the human body. It’s not only outstanding for total shoulder strength and health, but for our entire body. Some people may not agree with my view on this and would say it’s not a necessary movement. I would disagree that, but that’s another story.

However, it doesn’t mean that everyone should overhead press, even with the tremendous benefits that it offers.

Why would I say that?

I have talked and written a lot about the advantages of the overhead press. In my opinion and experience, the overhead press is extremely beneficial because it builds such functional upper body strength and enhances total body stability and integrity (*in an individual with healthy and asymptomatic shoulders).  

The shoulder is a dynamic and complex joint – and the press is an effective way to strengthen it.

This article, however, is not about the overhead press.

The information presented here is about individual anatomical variation in the human body.

So, let’s review a little basic anatomy of the shoulder.

This article is for your background information only and should NOT be considered diagnostic or medical advice in any way whatsoever. This article is purely educational about the anatomical differences in the human body.

Basic Anatomy of The Acromion.

The acromion is the bony end or distal part of your shoulder where part of your deltoid muscle attaches. This structure is part of the scapula (or shoulder blade) and it serves as the “roof” of the space in your shoulder joint called the subacromial (SA) space. It is in the SA space where shoulder impingement occurs as the supraspinatus muscle becomes painful and encroached with overhead motion.

But why? 

One reason for pain and shoulder disfunction can be attributed to an irregular shaped acromion.

While there are many possible problems and causes of shoulder pain, I’ll turn my attention towards one structural problem that could be considered a true culprit of overhead shoulder pain, decreased mobility, and reduced function.

Different Anatomy And Acromion Types.

In 1986, there was interesting research (1) in cadaver studies that revealed 3 different types of acromion shapes.

The 3 types found in the studies were:

Type 1 (Flat)

Type II (Curved)

Type III (Hooked)

The research further revealed that 17% of the shoulders had a Type I (or flat acromion). 43% had a Type II (or curved) acromion. And, 39% had the Type III (or hooked shape) acromion.

What exactly does this mean for you and I?

17% – FLAT

43% – CURVED

39% – HOOKED

Image courtesy of Paul Grilley

If you think about rotator cuff tears, a common problem for the shoulder joint, which type of acromion would you think may have the highest rate of tears (based on the shape and how this could encroach the shoulder joint space)?

If you guessed the hooked acromion, you’d be spot on.

A hooked acromion represented an alarming 70% of rotator cuff tears due to it’s irregular shape.

In a previous study (2) looking at patients with painful shoulders, it was found through MR imaging (MRI) that patients who had this Type-III (or hooked acromion) had higher rates of rotator cuff tears and shoulder impingement when compared to the control groups.

This suggests a strong correlation between a hooked acromion and a painful shoulder.

It is important to point out that correlation does not mean causation, so we have to keep that in mind. In this case, it would certainly make sense that there may be more shoulder issues based on the irregular structure of the shoulder and the reduced SA space.

Final Thoughts – What Does This All Mean?

I want to say again that in no way is this diagnostic with regards to any shoulder pain or problem you may be experiencing. This was not intended to help you self diagnose overhead shoulder pain or dysfunction.

The intent was to provide you background about individual anatomical variation in our own bodies.

We are all different, anatomically, physiologically, and genetically.

In this case, I have pointed out differences only in the shoulder bony anatomy.

Can you see how unique shapes and differences in joint structures could can limit function and cause pain and muscular problems?

As outlined, there can be different designs of our shoulder joint architecture and some of those differences may, unfortunately, be problematic.

If it’s uncomfortable or restricted with overhead motion, it is possible that could be an anatomical or structural problem.  Unfortunately, this type of issue won’t be resolved through corrective exercises (rotator cuff and/or scapular strengthening).

If you do have pain with overhead motion, the best thing you can do is seek out an expert health care professional to accurately assess, diagnose, and treat.

Certainly, corrective exercises are the best conservative approach to resolve pain and restore function, but in the case of a true structural problem (such as the Type III acromion), other appropriate medical interventions could be necessary.

Any painful situation, whether in the shoulder or any joint, requires appropriate medical assessment and intervention.

Remember, pain changes everything and needs to be accurately assessed to determine the root cause.

Hopefully, this has provided you some perspective and consideration about the anatomical differences in the human body and how this can impact our motion, our function, and, ultimately, our performance.

Our unique anatomical variations are not just limited to the shoulder.


1. The Athlete’s Shoulder by Dr. James Andrews and Kevin Wilk

2. Epstein, et al, Hooked Acromion : Prevalence On MR Images Of Painful Shoulders, Radiology, May 1993, 187 (2) 479-81

Scott Iardella, MPT, CSCS is a strength coach, athlete, and former “physio” who’s mission is to help men and women, regardless of age or background, forge their best, strongest self. Scott is the author of the book, The Edge of Strength.
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