Does changing the plane of abduction influence shoulder muscle recruitment patterns in healthy individuals?
METHODS
Observational laboratory study.


BACKGROUND
Abduction is a movement commonly used in the assessment of shoulder dysfunction and prescription of exercises to improve shoulder function. Abduction in the scapular and coronal planes are used interchangeably. It is not known if the activation of individual shoulder muscles differ between abduction performed in these planes and therefore, if they represent different tests/exercises.


OBJECTIVE
To quantify and compare the muscle activation patterns and levels for each shoulder muscle during abduction performed in the scapular plane with that performed in the coronal (scapular -30°) and scapular +30° planes.


METHODS
Electromyographic recordings were taken from eight shoulder muscles of fourteen healthy volunteers during shoulder abduction in the scapular and coronal planes and in a plane 30° anterior to the scapular plane (scapular +30°) at 50% of maximum load.


RESULTS
Similar average muscle activation levels were demonstrated during abduction in the scapular plane and within a 30° arc of this plane for all muscles except: middle deltoid (5% MVC higher activation in the coronal and 4% MVC lower activation in the scapular +30° plane) and upper trapezius (6% MVC lower activation in the scapular +30° plane). Activation patterns between planes for all muscles were similar (ICC(3,1) ≥ 0.87).


CONCLUSIONS
Abduction can be performed within a 30° arc of the scapular plane with no change in shoulder muscle activation patterns. Only middle deltoid activation levels change between the scapular and coronal planes and middle deltoid and upper trapezius between the scapular and scapular +30° planes.
Discipline of Biomedical Science, Sydney Medical School, The University of Sydney, Australia. Electronic address: darren.reed@sydney.edu.au.
Darren
D
Reed
Discipline of Biomedical Science, Sydney Medical School, The University of Sydney, Australia.
Ian
I
Cathers
Discipline of Exercise and Sport Science, Faculty of Health Sciences, The University of Sydney, Australia.
Mark
M
Halaki
Discipline of Biomedical Science, Sydney Medical School, The University of Sydney, Australia.
Karen A
KA
Ginn
D000293:Adolescent; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009135:Muscular Diseases / Q000534:rehabilitation*; D016059:Range of Motion, Articular / Q000502:physiology; D012540:Scapula / Q000503:physiopathology*; D000070599:Shoulder Injuries / Q000503:physiopathology* / Q000534:rehabilitation*; D012785:Shoulder Joint / Q000503:physiopathology*; D055815:Young Adult
Abduction; Electromyography; Muscle activation; Shoulder