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ORIGINAL RESEARCH

A Comparison of Change in 3D Scapular Kinematics with Maximal Contractions and Force Production with Scapular Muscle Tests Between Asymptomatic Overhead Athletes with and without Scapular Dyskinesis

Authors:  Seitz AL, McClelland RI, Jones WJ, Jean RA, Kardouni JR

The significance of scapular dyskinesis is being challenged due to a lack of the association with pain and ability to predict injury in athletic populations. However, it is unknown whether asymptomatic overhead athletes with dyskinesis cope by normalizing scapular position with higher demand activities.  The purpose of this study was to compare change in scapular kinematics during an unweighted active contraction to a maximal isometric contraction in asymptomatic overhead athletes with and without scapular dyskinesis. Secondarily, force generated with manual muscle tests were explored for differences and relationships with kinematics.  Twenty-five matched asymptomatic overhead athletes with (n=14) and without (n=11) scapular dyskinesis, defined with a reliable and validated clinical method, participated in this study. Three-dimensional scapular kinematics were evaluated in an active unweighted active movement condition, and during maximal isometric contractions at 90° of shoulder flexion. Isometric forces produced with lower trapezius and serratus anterior manual muscle tests were assessed with a hand held dynamometer.  Changes in scapular kinematics were compared between groups. Differences in force generated with manual muscle tests between groups and relationships with kinematics were explored.   Athletes with dyskinesis demonstrated greater deficits in scapular upward rotation with maximal contraction (p=<0.001), less external rotation (p=0.036) and weaker lower trapezius manual muscle test strength (p=0.031). Lower trapezius (p=0.003;r=0.57) and serratus anterior (p=0.042;r=0.41) manual muscle test strength deficits were fair to moderately associated with a lack of scapular upward rotation during maximal contraction.  The authors concluded that small to moderate changes in scapular kinematics are normal responses to a maximal contraction, but with scapular dyskinesis this response is accentuated. Athletes with dyskinesis generated less force with lower trapezius manual muscle testing compared to athletes without dyskinesis. Decreased strength with lower trapezius and serratus anterior manual muscle testing was also related to a lack of upward rotation in all athletes.

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