Humeral elevation reduces the dynamic control ratio of the shoulder muscles during internal rotation.
OBJECTIVE
To determine the differences in the dynamic control ratio of the glenohumeral joint rotators, during internal rotation at 20° and 60° of humeral elevation in the scapular plan. Dynamic control ratio (DCR) is defined as the ratio between eccentric action of the lateral rotators and the concentric action of the medial rotators.


METHODS
A cross-sectional laboratory study.


METHODS
Thirty asymptomatic participants (men n=14, women n=16, mean age=29.4±8.9years, BMI: 24.1±5.4) were tested. Peak torque generated by the concentric action of the MR and the eccentric action of the LR of the shoulder joint and the DCR were evaluated on the dominant arm using an isokinetic dynamometer at 20° and 60° of humeral elevation at a speed of 20°/s.


RESULTS
There was a significant decrease in the DCR at 60° humeral elevation when compared to 20° humeral elevation (p<0.05). This decrease was due to the significant decrease in eccentric peak torques at 60° humeral elevation when compared to 20° (p<0.05). However, there was no significant difference in the concentric peak torques between 20° and 60° (p>0.05).


CONCLUSIONS
The significant decrease in the DCR as a consequence of a decrease in the eccentric peak torque of the LR when the humerus is in a more elevated position suggests that the introduction of humeral elevation can be used as a progression for improving the eccentric action of the shoulder LR and subsequently the dynamic control of the shoulder.
School of Health Professions, Plymouth University, United Kingdom.
William
W
Howard
School of Health Professions, Plymouth University, United Kingdom.
Jonathan
J
Burgess
School of Health Professions, Plymouth University, United Kingdom.
Borut
B
Vrhovnik
School of Health Professions, Plymouth University, United Kingdom.
Christian
C
Stringer
Livewell Southwest, NHS, United Kingdom.
Sherrie T
ST
Choy
School of Health Professions, Plymouth University, United Kingdom.
Jonathan F
JF
Marsden
School of Health Professions, Plymouth University, United Kingdom.
Ingrid A
IA
Gedikoglou
Faculty of Sport & Health Sciences, University of St Mark & St John, United Kingdom. Electronic address: gshum@marjon.ac.uk.
Gary L
GL
Shum
D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006811:Humerus / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D017006:Rotator Cuff / Q000502:physiology*; D012540:Scapula; D012782:Shoulder / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*; D019415:Torque; D055815:Young Adult
Elevation; Isokinetic; Rotation; Shoulder