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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