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

Abstract

Background: Several glenohumeral joint (GHJ) positions have been recommended for assessing and correcting 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 change before and after an external humeral rotator muscle fatigue protocol in order to identify a position that shows maximum range of motion change.

Methods: ROM changes across four PST measurements were compared 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 (using a myotonometer) and external rotation force production (using hand-held dynamometry) were measured to verify muscle fatigue.

Results: There was a statistically significant interaction between measurement and condition (F = 2.47, p = 0.02). The planned one factor repeated measure ANOVA for each condition revealed that ROM change was statistically significant between PST measurements 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).

Conclusion: Immediate ROM reduction was observed 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.

Clinical relevance: Posterior muscle tightness may influence the internal rotation range of motion to a greater extent when measured in glenohumeral joint extension.

Levels of evidence: II-B.

Keywords: Glenohumeral joint; clinical measurement; horizontal adduction; internal rotation; muscle stiffness.

Figure 1.

Forearm rest angle measurement. The forearm rest angle is defined as the angle that the forearm makes relative to the vertical. Forearm position is considered externally rotated (dashed black line) if oriented lateral to vertical (solid red line) and internally rotated if oriented medial to vertical (dashed red line).

Figure 2.

Area under the curve (AUC) of a) Infraspinatus; and b) Teres minor. Y‐axis‐ area under the curve (in N.mm), X‐Axis‐ time points at which the stiffness was measured. * indicates statistically significant infraspinatus AUC reduction immediately after the external rotator fatigue. Error bars represent standard deviations.

Figure 3.

Forearm rest angle variation across the time points. * indicates statistically significant increase in forearm rest angle post fatigue and decrease in Infraspinatus area under the curve (AUC). The primary Y‐axis denotes the external rotation angle of the forearm; secondary Y‐axis denotes the Infraspinatus AUC in N.mm. Note that the secondary Y‐axis starts at 10 N.mm.