Sports Medicine Research: In the Lab & In the Field: Differences in Scapular Muscle Activation Ratios During Functional Shoulder Exercises (Sports Med Res)


Thursday, November 13, 2014

Differences in Scapular Muscle Activation Ratios During Functional Shoulder Exercises

Scapular muscle-activation ratios in patients with shoulder injuries during functional shoulder exercises.

Moeller CR, Huxel Bliven KC, Valier AR. J Athl Train. 2014;49(3):345-355. DOI: 10.4085/1062-6050-49.3.10

Take Home Message: Individuals with shoulder injuries had similar scapular muscle activation ratios as individuals without shoulder injuries during common exercises. It may be optimal to select the external rotation with scapular squeeze exercises because they had good activation of the middle trapezius, lower trapezius, and serratus anterior while minimizing over-activation of the upper trapezius.

Muscle activation during exercise can provide information regarding the type of injury that has been sustained. After an injury occurs, involved muscles are likely to lose strength compared to pre-injury levels. Scapular muscle activation is altered after glenohumeral injury, which may affect the stability and function of the shoulder. The authors of this study aimed to determine if activation ratios between the upper trapezius, middle trapezius, lower trapezius, and serratus anterior differed between athletes with glenohumeral injuries and healthy control athletes. Activation ratios were measured during functional exercises including the bow and arrow, external rotation with scapular squeeze, lawnmower, and robbery. This was a cross-sectional study, where 39 participants were assigned to one of two groups: 20 participants with glenohumeral injuries and 19 matched healthy control participants. The participants performed the concentric phase of the functional exercises over a period three seconds and muscle activity was recorded with surface electromyography. They performed 5 acceptable repetitions of each exercise and the researchers used the middle three repetitions for their analyses. The activation ratios measured included the upper trapezius:middle trapezius, upper trapezius:lower trapezius, and upper trapezius:serratus anterior. The upper trapezius, middle trapezius and lower trapezius muscles saw the highest activation during the bow-and-arrow exercise and the serratus anterior had the highest activation during the external rotation with scapular squeeze. The upper trapezius:middle trapezius ratio and the upper trapezius:lower trapezius ratio were greatest in both groups during the bow and arrow and robbery exercises. Overall, there were no differences for the muscle activation ratios between the two groups.

The authors examined muscle activation in individuals with glenohumeral injuries and non-injured individuals, reporting that there are no differences in the muscle activation during typical functional exercises. As a clinician, this study can benefit the rehabilitation process by focusing on activating the proper muscles. Having the athlete focus on individual muscles rather than the movement of the exercise may benefit from higher activation from the involved muscles. The authors stated that clinicians should be cautious with the bow and arrow exercise because of hyperactivity in upper trapezius compared with the middle or lower trapezius. With high ratios of incorrect muscle activation, the participants may not receive the proper benefit from the work that gives wasted movement. In contrast, clinicians may want to select exercises like the external rotation with scapular squeeze, lawnmower, and robbery that promote activation of the middle and lower trapezius or serratus anterior while minimizing upper trapezius activation. It would be interesting to follow-up on this study by assessing differences in muscle strength in similar participants. In doing this, clinicians could assess weakness of the shoulder muscles to improve the strength in injured athletes. If the tests show that one or two muscles are consistently weak among those with the same injuries, it may help clinicians to work with patients, in particular, overhead athletes to proactively limit the number of glenohumeral injuries that occur. Clinicians can use these results to improve patient care by emphasizing proper exercise selection, positioning, and form. With correct exercises and form, individuals completing rehabilitation exercises could have an enhanced recovery process compared to incorrect form and positioning.

Questions for Discussion: Do you think we could expect to see similar results in other muscles surrounding the glenohumeral joint? As rehabilitation providers, do you focus on correct position during exercises, proper muscle activation and increased strength in athletes?

Written by: Kaitlyn Griffith and Vince Claudio
Reviewed by: Kim Pritchard

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Anonymous said...

Hi. Can you clarify the results of this study? From my understanding the key points in the article state that the bow and arrow exercise did cause over-activation of the upper trap

Jeffrey Driban said...

Thank you for catching the error. The second paragraph correctly noted that caution should be used with the bow and arrow exercise b/c it caused over-activation of the upper trap. A good option would be the external rotation with scapular squeeze. The key take home message has been updated above. Thanks!

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