P B de Witte1, S Werner2, L M ter Braak2, H E J Veeger2, R G H H Nelissen3, J H de Groot4. 1. 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. 2. Faculty of Human Movement Sciences, VU University of Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands. 3. Department of Orthopaedics, Leiden University Medical Center, Postzone J11R, Postbus 9600, 2300 RC Leiden, The Netherlands. 4. 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.
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. CONCLUSION: 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.
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. CONCLUSION: 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.
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