Evaluation of shoulder internal rotator muscle strength in baseball players with physical signs of glenohumeral joint instability

OBJECTIVES: To identify whether subjects with glenohumeral translational instability present with a strength deficit in their internal rotator musculature, and therefore to determine if general strengthening exercises are warranted for the management of this condition.

METHODS: Eighteen male baseball players were allocated to two groups on the basis of expert clinical evaluation of the presence (n=8) or absence (n=10) of shoulder translational instability. A strain gauge was used to calculate the force generated during maximal isometric internal rotation contractions in neutral shoulder rotation and 30 degrees of internal rotation.

RESULTS: The Mann-Whitney test identified no significant difference in force production during the maximum contractions in neutral rotation between the two subject groups. In the position of 30 degrees shoulder internal rotation, subjects with glenohumeral translational instability produced significantly greater force than the control group (p<0.05).

CONCLUSIONS: High load strength testing cannot be used as a diagnostic tool to identify people with glenohumeral instability. Similarly, heavy resistance strengthening exercises for the internal rotator musculature are not warranted during rehabilitation.