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