Sports Medicine Research: In the Lab & In the Field: Shoulder Force Couples – How do They Function Throughout Rehab Exercises? (Sports Med Res)


Friday, December 16, 2011

Shoulder Force Couples – How do They Function Throughout Rehab Exercises?

Rotator-cuff muscle-recruitment strategies during shoulder rehabilitation exercises.

Swanik KA, Huxel Bliven K, Swanik CB. J Sport Rehabil. 2011 Nov;20(4):471-86.

Do you remember diving into your first upper extremity therapeutic exercise class? Looking back, it seems like from day one that we were taught to hammer the rotator cuff for any and all shoulder injuries. While we were wrestling to understand the dynamic stabilization aspect, one thing that wasn't so readily taught or considered when constructing a rehabilitation protocol is what the magnitude of muscle activation might be for these muscles throughout the entire motion arc of a selected exercise. Is it possible that we should be even more judicious about which exercises are selected, and when they are placed within a rehab protocol? In this study Swanik et al. investigated muscle coactivation levels and coactivation patterns of the subscapularis, infraspinatus, and teres minor throughout the range of motion (ROM) of 4 commonly utilized therapeutic exercises. These muscles make up the force couple which opposes anterior-posterior glenohumeral joint translation. Muscle activity of the supraspinatus was also recorded. For this study, 33 healthy, physically active men (~20 years old) were recruited. The dominant arm was tested on each and was defined as the extremity that they would use to throw a ball (right, n = 26; left, n = 7). All subjects then completed bouts of D2 PNF pattern with resistive tubing, kneeling 90/90 pitchback with a 1.1 kg plyoball, a push up plus, and horizontal ab/adduction on a slide board while on their hands and knees. Cotton coverings were placed over the subjects hands to decrease friction throughout the exercise's ROM. The selected muscles of each subject were connected to fine wire intramuscular electrodes to obtain the muscular activation data. Data obtained showed that muscle co-activation levels ranged anywhere from 47 to 60% for the selected exercises with no significant differences between the exercises. The authors did find significant differences in coactivation patterns, with the most noticeable instances occurring at the initiation of the exercise (first 0 to 20% of exercise completion) and when the glenohumeral joint was in a vulnerable position at end range ROM (flexion, abduction, and/or external rotation). Furthermore, the subscapularis was the only muscle to exhibit significant increases in muscle activation when examining its individual activation for each exercise. The two exercises showing the most subscapularis recruitment were the push-up plus and the slide board exercise. The push-up plus was the only exercise for the subscapularis that demonstrated a significant increase in muscle recruitment. The slide board exercise exhibited the second most supraspinatus activation, but this did not reach statistical significance.

This article is interesting for a few reasons. First and foremost, it is truly one of the first articles to determine what is going on at the muscular level throughout an exercise's entire ROM. While it does have some short-comings (e.g., including healthy males only), the results allow us to quantitatively see what is occurring. As clinicians we can use this information to better structure our rehab protocols by initiating the proper exercises at the proper time during the patients recovery and progression. Knowing which exercises your patient will get the best results from and where in the motion they will get the most out of those exercises during their utilization is invaluable. Future studies will potentially need to focus on other exercises so that clinicians can have a broader knowledge base in terms of muscular activity over the entire ROM. What are your thoughts on this study? Would you like to have seen them incorporate any injured subjects? If you are utilizing closed chain exercises in shoulder protocols, are you inclined to use them even more, based upon these results? If you aren't using closed chain exercises, will you consider using them now? 

Written by:  Mark Rice
Reviewed by:  Stephen Thomas

Related Posts:
The Influence of Arm & Shoulder Position on 3 Clinical Tests for Subscapularis Injuries

Swanik KA, Huxel Bliven K, & Swanik CB (2011). Rotator-cuff muscle-recruitment strategies during shoulder rehabilitation exercises. Journal of Sport Rehabilitation, 20 (4), 471-86 PMID: 22012500


MEShiresATC said...

This is a good start researching the activation/co-activation of the RC.

I think they "missed" out on capturing the force coupling lower/upper trap and serratus in these positions, to add into the RC and GH stabiliztion.

Mark A. Rice said...

Thank you for reading and commenting. While you'd be hard pressed to find two bigger proponents of the scapula's role in overhead function than Steve Thomas (co-SMR founder) and myself, I wouldn't necessarily say that they "missed" out.

Yes, the authors looked solely at what effect these exercises would have on the AP resisting force couple. I'd contend that when delving into new areas regarding shoulder function I think that more often than not AP GH joint stability is the foundational aspect that needs be scrutinized. Once that is established , other authors will branch off/spin off and investigate other areas, including the serratus/low trap relativity.

While I'd love to have seen the serratus and low trap addressed in this study, it leaves the door open for future studies, which is always the goal for studies like this.

Pearl Coleshill said...

I like where this research is going. As newly certified athletic trainer, I am still familiarizing myself with effective exercises within my rehab protocols.

Mark, I really do remember my first upper extremity class... and I do remember flying through it as my professor tried her best to fit everything in to one semester. It's hard to constantly be a sponge to all of the information, and it's equally as hard to keep it absorbed. Research like this helps keep us up-to-date, and most of all, on top of our game as health professionals.

It would have been nice to see them incorporate injured subjects, but like you said, it saves room for further studies. Based on this research I will be sure to use more CC exercises in my protocols!

There's no better time than now to go outside our comfort zones to learn and apply new strategies that can benefit our athletes.

Mark A. Rice said...

Pearl, thank you for reading and posting. I'm glad to see that we have a new professional contributing. I couldn't agree with you more about getting outside of our comfort zones. When you get down to it, the bulk of the info that you learned in school will change drastically, and if you don't change and grow and continue to learn, you will only be as good as you were on graduation day.

I'd like to complement you for analyzing what you already do and looking to make it even better. That's the whole purpose of SMR, to make the readers better and more informed clinicians.

Please feel free to link to our Facebook, Twitter, Linkedin and Google+ pages. You have already proved that you are willing to step out of your comfort zone, so please share SMR with your colleagues, classmates and friends to get them out of theirs' .

Thanks, again!

personal injury lawyers new york city said...

Nice description on shoulder force couple...

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