Distance and 3-Dimensional Scapular Position Change After Overhead Muscle

Maenhout A1, Dhooge F, Van
Herzeele M, Palmans T, Cools A. J Athl Train. 2015 Jan 16. [Epub ahead of

Home Message: After overhead shoulder fatigue, healthy individuals have an
increase in acromiohumeral distance and altered scapular position, consistent
with a protective, impingement-sparing situation.

Muscle fatigue due to
overhead sports has been hypothesized to contribute to shoulder impingement
(and subsequent rotator cuff pathology) by altering the position of the scapula
and narrowing the subacromial space. 
However, conflicting evidence exists in the literature and as a result,
no consensus has been established.  This
may be due to the fact that most investigators use different fatiguing
protocols that do not resemble overhead sports activity and only indirectly
measure the subacromial space.  Therefore,
the objective of this study was to assess the effect of a fatigue protocol that
resembled overhead sports activity on scapular position and acromiohumeral distance,
which is indicative of the amount of subacromial space.  For this study, a total of 29 healthy
recreational overhead athletes (14 men, 15 women, ~22 years of age) were tested
at 3 elevation positions (0⁰, 45⁰, and 60⁰ of abduction) before and after a
shoulder muscle fatiguing protocol.  The
fatigue protocol consisted of repeated shoulder internal and external rotation with
resistance while the shoulder was at 90 degrees of abduction. The authors
measured acromiohumeral distance (using ultrasound) and scapular position
(using an electromagnetic motion-tracking system).  The researchers demonstrated an increased acromiohumeral
distance following fatigue when the upper extremity was actively positioned at
45⁰ or
60⁰ of
abduction.  The scapular position also
changed after fatigue to a more externally and upwardly rotated position at 45⁰ or 60⁰ of abduction and
more posteriorly tilted at all angles. 

Results from this study
suggest that muscle fatigue following overhead activity increases the acromiohumeral
distance and leads to a more externally and upwardly rotated and posteriorly
tilted scapula.  These changes are
surprising and suggest that overhead sports fatigue does not narrow the acromiohumeral
distance but actually enlarges it, indicative of an impingement-sparing
situation.  It is important to note that acromiohumeral
distance measurements were only performed at low angles (below 90⁰ of abduction)
while the fatiguing protocol was performed at 90⁰ of abduction.  It would be interesting to further
investigate changes in acromiohumeral distance at larger angles.  Another consideration is that the population
chosen for this activity were young, healthy individuals with no history of
shoulder pathology.  This specific
population seems to be able to compensate effectively following muscle fatigue
while it is possible that older or injured populations may not.  In addition, the muscle fatiguing protocol only
looked at one bout of fatigue but it would be interesting to see how the
results would change if fatigue was repeated. 
The researchers also indicate that their protocol may have specifically
targeted the glenohumeral muscles, allowing sufficient compensation by the
scapulothoracic muscles.  It is possible
that greater fatigue of the scapulothoracic muscles may not spare the shoulder
from impingement.  This study necessitates
further clinical studies to investigate the role of impingement in the
development of rotator cuff pathology in overhead athletes. In the meantime,
this study serves as a nice reminder that we should carefully evaluate
fatiguing protocols and patient populations used in each study before running
to conclusions on this important topic. To determine if one of our athletes is
at risk it may be ideal to evaluate him/her before and after practice or a game
to see how that specific individual is responding to their activities.

for Discussion: If
distance and scapular position are not to
blame, what other factors do you think contribute to rotator cuff pathology in
this population? Do you think
acromiohumeral distance and scapular position would be compromised in a different population?

Written by: Katie Reuther
Reviewed by: Jeffrey

Related Posts:

Maenhout, A., Dhooge, F., Van Herzeele, M., Palmans, T., & Cools, A. (2015). Acromiohumeral Distance and 3-Dimensional Scapular Position Change After Overhead Muscle Fatigue Journal of Athletic Training DOI: 10.4085/1062-6050-49.3.92