If there is one thing that I would say is the most important concept to understand regarding the shoulder, it is simply that you can not work the rotator cuff to failure as rotator cuff fatigue causes superior humeral head migration and subacromial impingement. That is it, I just summarized the role of the rotator cuff in one sentence, albeit a long sentence!
I talk about this concept all the time including a past post on humeral head biomechanics after rotator cuff fatigue, my Optimal Shoulder Performance DVD with Eric Cressey, as well as an entire week on rotator cuff injuries in my online shoulder CEU program. Yet, I still read and see people performing exercises designed to “burn out” the cuff, or build endurance my “working the cuff to failure.”
This doesn’t work. You can not work the rotator cuff to failure.
Rotator Cuff Fatigue Increases Superior Humeral Head Migration
Another recent study by Jaclyn Chopp from the Journal of Shoulder Elbow Surgery again contributes evidence to this concept. The study examined the amount of superior humeral head migration during arm elevation in the scapular plane before and after fatiguing the rotator cuff. The examiners fatigued the rotator cuff by performing a repetitive overhead lifting task that involved lifting an object in the following fashion:
- Lifting an object from 45 degrees to 135 degrees of sagittal plane elevation
- Then, slowly lowering the object in the same plane
- Then, externally rotating the arm and lifting in the coronal plane
- Then, slowly lowering the object again and internally rotating back into the original start position
- Lastly, they also performed 5 second static holds at 90 degrees abduction with the same weight every minute.
As you can see, I like their fatigue protocol as it combines flexion, abduction, external rotation, and internal rotation of the shoulder, plus they threw in the commonly performed static hold at 90 degrees abduction. The weight they lifted was 15% of their maximal lift, so certainly not that heavy and a good replication of a functional activity.
In the pre-fatigued state, the shoulder demonstrated normal biomechanics of a mild amount of superior humeral head migration that eventually stopped and centered the humeral head within the glenoid fossa. This is normal, as the humeral head actually sits inferior to the center of the glenoid in the resting position, likely due to gravity. So, you can see in the table below that the humeral head rises up a little and then actually migrated inferiorly as the arm is elevated.
In the fatigued state, the humeral head continued to migrated superiorly and never started to move inferiorly, effectively decreasing the subacromial space and potentially leading to shoulder impingement.
More evidence indeed to support the concept that the rotator cuff is so important in providing dynamic stability of the shoulder, even during simple tasks, that you can not work it to failure. So think of this next time you want to attempt to work the cuff to failure. Doing so will increase superior humeral head migration and increase subacromial impingement. So after that exercise, every time you pick up your arm for the rest of the day, you are causing some subacromial impingement.
So consider this a call to action, stop working the cuff to failure or performing burn out sets for the rotator cuff (and the back too, but that is another post…). These muscles don’t work this way. I continue to stick to sets of 10 repetitions for shoulder exercises. I am also very careful when trying to build endurance in the rotator cuff, assuring that the person’s overall shoulder workload is not too high when focusing on endurance.
The last thing you want to do is cause rotator cuff fatigue, superior humeral head migration, or subacromial impingement.
