Fatigue of the Rotator Cuff Causes Altered Shoulder Mechanics and Impingement

Another interesting article from the most recent issue of Journal of Athletic Training on rotator cuff fatigue and glenohumeral kinematics. In this study, the authors used dynamic fluroscopic video to assess superior humeral head migration in 20 asymptomatic subjects before and after fatigue of the rotator cuff. The assessment of migration during a dynamic activity is a fairly novel approach as previous studies that have attempted to quantify superior humeral head translation have used static imaging such as radiographs and MRI.

During the study the authors used the prone horizontal abduction (with thumbs up) exercise to fatigue the cuff until there was a documented decrease of at least 40% strength. This was an important part of the study, as a reader I want to be sure that fatigue had occurred and a 40% drop is significant for me. I must say, though, that I wish the authors had performed a more specific rotator cuff exercise, such as simple external rotation. The prone exercise has shown EMG activity of the cuff but also the deltoid and scapula musculature.

Results of the study show that humeral head migration increased by an average of 0.79mm during elevation in a fatigued state. While this seems small, keep in mind that the average subacromial space is between 2mm and 14mm in healthy subjects (can be about 50% smaller in pathological patients), thus reducing subacromial space by up to 40%!

Clinical Implications

RTC fatigue can lead to impingement
. An interesting component of the article that the authors did not bring up in their discussion was that the humeral head actually migrated inferior prior to fatigue as the RTC acted to maintain the humeral head within the glenoid fossa as the deltoid provided a superior orientated force vector. After the fatigue, not only did the humeral head not migrate inferior, it moved superiorly. This has obvious implications for subacromial impingement. Both strength and endurance of the cuff should be addressed in rehabilitation, makes sense why a deconditioned person so much more likely to develop shoulder impingement.

The RTC should never be worked to failure. The fatigue protocol used by the authors lasted for less than 90 seconds. That is all it took for the RTC to loose 54% of it’s strength. Now think about that last time you had a patient come to you with “impingement” that reported playing tennis or golf for the first time in months, or even more simply, painting a room in their house. With only 90 seconds of activity the cuff fatigue enough to decrease your subacromial space by up to 40%. What should your treatment be for that patient? Minimize the initial inflammation, work on cuff strength & endurance but by all means, DON’T work the cuff to failure.

The rotator cuff should NEVER be worked to failure!

I never understood this training technique. If you work the cuff to failure than what is going to dynamically stabilize the humeral head later that day when you a reaching overhead?

As always, please comment with your thoughts and experience!

 

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10 Responses to “Fatigue of the Rotator Cuff Causes Altered Shoulder Mechanics and Impingement”

  1. Mike, do you advocate having patients avoid “the burn” or fatiguing sensation in the upper arm/shoulder when performing external rotation exercises. Should we avoid this altogether when exercising our patients?

    Thanks,
    Ernie

  2. @ Ernie – Good question. The sensation of a “burn” is actually pretty common in my experience. I even do RTC exercises myself and know exactly what the “burn” is that patients describe. For me, If there is a burn at the end of the set, I am not too concerned if I am building in rest between sets and controlling the volume of sets and reps. What I would recommend avoiding is when a patient feels a “burn” and demonstrates poor kinematic or compensation during the exercise. That is a sign that the cuff is too fatigue and you may work through cuff inhibition.

    MR

  3. Mike,
    I think a lot about the timing of rotator cuff exercises with pitchers. Do you suggest a pitcher perform his rotator cuff program immediately following pitching or could this cause more harm than good? Would you suggest more be done the day after or the day of his bullpen? What volume of pitching do you think is necessary to cause enough RTC fatigue to make exercise counter productive, or is it, like most things, completely individualized to the athlete?

  4. Hi Adam, all good questions, i’ll start towards the end of the comment, regarding the volume. This is individualized based on each player. I know that sounds like a lame response, but that is why pitchers have roles. Obviously, it is possible to throw 120 pitches in a game, starters do it all the time because they are accustomed to it. Relievers can not. They will vary for when they fatigue. Fatigue studies out of Tim Uhl’s group showed that proprioception was altered after ~65 pitches. I don’t do exercises after they pitch. Seems unproductive to me. The analogy of running some sprints after running a marathon comes to mind. I do think it is different after a pen, because volume is much lower. Exercises are fine for me after a pen.

    Just my thoughts, I know that other teams do different things. What do you do Adam?

  5. Mr Rehabilitative Physical Therapies December 30, 2009 at 1:21 am

    Thanks for Very nice post with a ton of informative information. I really appreciate the fact that you approach these topics from a stand point of knowledge and information
    instead of the typical “I think” mentality that you see so much on the internet these days.

  6. Great post. I appreciate the information.

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