A comparison of range of motion change across four posterior shoulder tightness measurements after external rotator fatigue.    

Authors: Dashottar A, Costantini O, Borstad J

Several glenohumeral joint  (GHJ) positions have been recommended for assessing and treating posterior shoulder tightness (PST). However, there is no agreement on which position is better for differentiating posterior muscle tightness from posterior capsular tightness.  The purpose of this study was to compare the range of motion before and after an external humeral rotator muscle fatigue protocol in order to identify a position that shows maximum range of motion change.  The authors compared ROM changes across four PST measurements before, immediately after, at 24 hours after, and 48 hours after an external rotator fatigue protocol. Muscle stiffness of the infraspinatus and the teres minor (measured using a myotonometer) and external rotation force production (measured using hand-held dynamometry) were assessed to verify muscle fatigue.  The authors found that there was a statistically significant interaction between measurement position and condition (F= 2.47, p= 0.02). The one factor repeated measure ANOVA for each condition revealed that ROM change was statistically significantly different between measurement positions for all conditions. Post hoc comparisons indicated statistically significant greater overall ROM changes in a measurement combining GHJ extension and internal rotation compared to other tested measurements. There was also a main effect of time on infraspinatus muscle stiffness (F= 10.5, p<0.0001). Post hoc comparison indicated a statistically significant increase in infraspinatus stiffness immediately after the fatigue protocol (p<0.05).  Therefore, the authors concluded that immediate ROM reduction occurred across all the measurements except horizontal adduction (HAD). Maximum ROM reduction after an external rotation fatigue protocol was measured in a position of GHJ extension.   Posterior muscle tightness may influence the internal rotation range of motion to a greater extent when measured in glenohumeral joint extension.

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