Does Isometric Shoulder Strength Correlate to Shoulder Endurance?

Context: Shoulder strength in relation to endurance is an understudied topic in the field of sports medicine. Shoulder injuries are common and often result from the repetitive nature of overhead sports. The benefit of a strong correlation would ultimately help aid rehabilitation and injury prevention programs for overhead athletes.

Objective: The purpose of this study is to determine if there is a direct correlation between rotator cuff strength and shoulder endurance for internal and external rotation 

Design: Qualitative study

Participants: Twenty-three male collegiate students between 18-30 years old without a shoulder injury or pain within the last 12 months.

Data Collection and Analysis: Subjects were sampled through convenience sampling and were screened to meet inclusion criteria. The subject’s dominant arm was tested for both strength and endurance of internal rotation of subscapularis and external rotation of infraspinatus and teres minor. Subjects were randomly assigned to testing order. Tools included a hand-held dynamometer to test strength and a pressure biofeedback unit to test endurance. Measurements for strength and endurance were tested in three positions of shoulder abduction (0, 30, and 90 degrees) for internal rotation and external rotation. Data was evaluated through a Pearson correlation and Spearman Rank correlation.

Results: Results showed overall weak correlation between shoulder endurance and strength. The highest correlations were at 45 degrees shoulder abduction and external rotation (r=0.38) and 45 degrees with internal rotation (r=0.21). The lowest correlation was at 0 degrees of internal rotation (r=-0.03) 

Conclusion: There were not enough significant results to suggest a correlation between shoulder strength and endurance. This study opened up to further research with modifications in the approach and use of more standardized devices of measurement.