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

Background: 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. Hypothesis/Purpose: The purpose of this study was to compare change in scapular kinematics from an active unweighted 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. Study Design: Cross-sectional laboratory study Methods: 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 condition, and during maximal isometric contractions at 90 degrees of shoulder flexion. Isometric force produced with lower trapezius and serratus anterior manual muscle tests were assessed with a 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. Results: 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. Conclusion: 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 generate 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.