title: The Supraspinatus and the Deltoid - not just two arm elevators.
abstract: BACKGROUND
  The debate on the clinical and functional role of the Supraspinatus in relation to the Deltoid necessitates experimental assessment of their contributions to arm elevation. Our goal was to evaluate the responses of both muscles to increased elevation moment loading.
  
  
  METHODS
  Twenty-three healthy volunteers applied 30N elevation forces at the proximal and distal humerus, resulting in small and large glenohumeral elevation moment tasks. The responses of the Deltoid and Supraspinatus were recorded with surface and fine-wire electromyography, quantified by (EMGdistal-EMGproximal), and normalized by the summed activations (EMGdistal+EMGproximal) to RMuscle ratios.
  
  
  RESULTS
  Deltoid activity increased with large elevation moment loading (RDE=.11, 95%-CI [.06-.16]). Surprisingly, there was no significant average increase in Supraspinatus activation (RSSp=.06, 95%-CI [-.08 to .20]) and its response was significantly more variable (Levene's test, F=11.7, p<.001). There was an inverse association between the responses (ß=-1.02, 95%-CI [-2.37 to .32]), indicating a potential complementary function of the Supraspinatus to the Deltoid.
  
  
  CONCLUSIONS
  The Deltoid contributes to the glenohumeral elevation moment, but the contribution of the Supraspinatus is variable. We speculate there is inter-individual or intra-muscular function variability for the Supraspinatus, which may be related to the frequently reported variations in symptoms and treatment outcome of Supraspinatus pathologies.
authors.affiliation: Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics and Rehabilitation Medicine, Leiden University Medical Center, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, The Netherlands; Department of Orthopaedics, Leiden University Medical Center, Postzone J11R, Postbus 9600, 2300 RC Leiden, The Netherlands. Electronic address: P.B.de_witte@lumc.nl.
authors.forename: P B
authors.initials: PB
authors.lastname: de Witte
authors.affiliation: Faculty of Human Movement Sciences, VU University of Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Werner
authors.affiliation: Faculty of Human Movement Sciences, VU University of Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.
authors.forename: L M
authors.initials: LM
authors.lastname: ter Braak
authors.affiliation: Faculty of Human Movement Sciences, VU University of Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.
authors.forename: H E J
authors.initials: HE
authors.lastname: Veeger
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center, Postzone J11R, Postbus 9600, 2300 RC Leiden, The Netherlands.
authors.forename: R G H H
authors.initials: RG
authors.lastname: Nelissen
authors.affiliation: Laboratory for Kinematics and Neuromechanics, Department of Orthopaedics and Rehabilitation Medicine, Leiden University Medical Center, Postzone B0-Q, Postbus 9600, 2300 RC Leiden, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: de Groot
mesh_terms: D000293:Adolescent; D000328:Adult; D001132:Arm / Q000502:physiology*; D057645:Deltoid Muscle / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D017006:Rotator Cuff / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult
keywords: Abduction; Coordination; Deltoid muscle; Electromyography; Fine-wire; Rotator cuff; Supraspinatus muscle