evaluation and treatment of shoulder impingement

Rotator Cuff Fatigue Increases Superior Humeral Head Migration

shoulder impingementIf 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.

rotator cuff fatigue

superior humeral head migration

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.

22 replies
  1. Northernontariogirl
    Northernontariogirl says:

    In February I developed superior humeral head migration and subacromial impingement due to swimming for exercise. I have tried PT and athletic therapy and while my shoulder is stronger and more flexible it’s had zero effect on the impingement. I am seeing a different physiotherapist Friday. Any suggestions for how to make some progress? I miss swimming!!!

  2. Nathan
    Nathan says:

    What about people who have underactive Infraspinatus and teres minor due to postural issues? I usually do 12-20 reps and am not doing heavy lifting. Just rehab work. Dont you think there is an exception

  3. Jonah Frost
    Jonah Frost says:

    Mike, I recently had a tenodesis of my proximal biceps tendon. Prior to my surrey I could feel my humeral head clicking as it glided over my labrum. I returned to the gym 8 months post-op and I still feel the clicking. Is it possible that I have a rotator issue that was missed by the M.D. or is it more likely the absence of a biceps tendon that is causing this.

  4. Chris
    Chris says:

    Hi Mike,

    How much fatigue is too much? Is stopping one rep short of failure ok? Should I stop before losing any acceleration or is it okay to have a slower rep before termination of the set? Are you sure the same problems will occur when doing isolation exercises like rotations with a cable?

    Does this mean that no one should ever accumulate fatigue when doing shoulders exercises, even with healthy shoulders? That seems a tad excessive to me. How are you supposed to strengthen and hypertrophy the muscles then?

    Is this just an endurance strength related problem, or is fatigue to be avoided when traning for max strength with lower reps as well? It seems to me that a lot of strength related sports would be impossible to do if one were to take this seriously.

    • Mike Reinold
      Mike Reinold says:

      Chris, will definitely happen with isolated exercises, try it, do as many reps as you can and post back with how you felt after and how many hours it took to come back!

      The cuff works different than muscles like the quad. You build strength and endurance through frequency, not within one exercise session. You dont want to work until failure and then take 3 days off, would rather work daily etc.

  5. Saboora Chaudhry
    Saboora Chaudhry says:

    Hey Mike,

    A question I have is how to apply this to the industrial setting. I work with people that primarily overload their shoulders bucking, drilling, riveting, etc, but do so ~6 hours a day, every day. What would you recommend as far as when they should do their shoulder strengthening exercises, since they’re fatiguing their shoulders daily?


    • Mike Reinold
      Mike Reinold says:

      Just like anything else, the body adapts. This isnt far off from an overhead athlete that works their shoulder for a couple of hours a day (less time but more velocity). They still need strong cuffs, challenge is to find a time that they can get strong and recover to work, same as athletics.

  6. Walt Lingerfelt
    Walt Lingerfelt says:

    Good critical appraisal by Stephen. Theoretically it certainly does make since that fatiguing the cuff in a shoulder that may only have 3-5 mm “error room” (before impingement occurs) will only cause increased translation thus greater impingement. However, given the RTC’s function of an endurance function it would seem reasonable to train it in such a way. Again, it becomes a delicate balance between not working enough and over working. It would be near impossible to find the correct balance through research for numerous reasons but I suppose one of the best ways we can help is educating patients to avoid significant OH activities particularly after exercise and symptomatically adjust treatment based on response.

  7. Stephen Thomas, PhD, ATC
    Stephen Thomas, PhD, ATC says:

    This is an interesting study, however the methods could have been improved. The fatigue protocol did not isolate the rotator cuff. It was more of a general shoulder fatigue. The protocol that was used may have also fatigued the scapular stabilizers, which could have affected the position of the humeral head. Second, using surface EMG to measure muscle activity of the deep rotator cuff introduces errors due to muscle cross talk and this could directly affect the fatigue values. Third, the radiograph technique for measuring humeral head position was limited to the superior and inferior directions. Since impingement is thought to mainly be in the anterior/superior direction it would have been interesting to have the other direction. In addition, there was only a 1mm increase in superior migration and test-re-test reliability was not reported. As with any manual technique there are errors that can be produced with subject positioning, arm positioning, radiograph position, calculation of the geometric center of the glenoid. All of these will produce even minimal error so the question that arises is this 1mm increase clinically significant. I would have also liked to have a measure of sub-acromial space since they should be able to measure that from the radiographs. If that was decreased then it would be further validation of their measurement technique. I agree with the previous comments as well. We know from previous work that recovery from fatigue typically occurs quickly. (This does not take into account any DOMS that has been produced from the fatigue session and that would be another question to answer) So the question of exactly how long before the humeral head assumes its normal position would be beneficial. That would have been a nice and easy addition to the study with just another radiograph measurement 1 hour after the fatigue was performed. Sorry for being long winded, the researcher in me came out!

    • Mike Reinold
      Mike Reinold says:

      Stephen, great thoughts, THANKS for sharing! I do think 1 mm is significant. I think 0.00000001 mm is significant! But seriously, all you need to do is disrupt the normal homeostasis of the cuff and you start and inflammation-inhibition cycle.

      In regard to some of your other comments, realize that fatigue does not cause a static change in position, but a dynamic change, meaning the humeral head drifts upward when you elevate the arm. Also, EMG was a small part of this study, so the fact they used surface doesnt bother me.

      Agree on the fatigue and 1 hour x-ray concept… perhaps that is our next study!

  8. Katherine
    Katherine says:

    So to build endurance when only using sets of 10, how many sets do you usually do and how do you recommend going about building endurance?

  9. Scott Ensell
    Scott Ensell says:

    Good question by Dan. Beat me to it actually.

    Here is another one though:
    If we are using sets of 10 reps, is that enough to increase the muscular endurance and in turn, delay the onset of the fatigue that then causes the humeral head migration/impingement?

    • Mike Reinold
      Mike Reinold says:

      Scott, this is anecdotal at this time, but effective for me. I havent had any issues achieving my goals using sets of 10. Has it been effective for you?

  10. Dan
    Dan says:

    A good follow-up study would be the recovery rate of the RTC. How long does the cuff need to recover before it limits migration again?

    • Mike Reinold
      Mike Reinold says:

      Dan – excellent question, assume there would be a time response that correlates to the amount of fatigue. Try it! Do as many ER tubing reps as you can (when we play this game, we often get into the 70’s or 80’s) and see! Later that night you wont be able to pick up your arm w/o a shrug and pinch! Also, hard to study because if you then pinch too much and inflame, you’ll get cuff inhibition on top of it that will make it seem like you are still “fatigued.” Good question, though.

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