Reliability and Validity of Measuring Shoulder Internal and External Rotation Strength in Volleyball Specific...

Area of Science:

• Sports Medicine
• Biomechanics
• Physical Therapy

Background:

• Overhead athletes frequently experience shoulder injuries, with rotator cuff issues being common and linked to muscle weakness.
• Accurate measurement of rotator cuff strength in sport-specific positions is crucial for effective sports physical therapy.

Purpose of the Study:

• To evaluate the inter- and intra-tester reliability of measuring shoulder internal rotation (IR) and external rotation (ER) strength at 130° abduction.
• To compare the reliability of the 130° abduction position with the traditional 90°/90° position.
• To assess the concurrent validity between an Isokinetic Dynamometer (IKD) and a hand-held dynamometer (HHD).

Main Methods:

• Twenty-five healthy participants underwent maximal isometric shoulder IR and ER strength testing at 90° and 130° abduction.
• Measurements were taken using an IKD and an HHD, with repeat HHD testing after 7-14 days.
• Intraclass Correlation Coefficients (ICC) and Bland-Altman plots were used to analyze reliability and agreement.

Main Results:

• Good to excellent inter- and intra-rater reliability (ICC > 0.8) was found for HHD strength testing at both shoulder positions.
• Concurrent validity between the HHD and IKD was poor to moderate (ICC 0.1-0.4).
• Bland-Altman plots indicated that the differences in strength measurements between the HHD and IKD were within acceptable limits of agreement.

Conclusions:

• Shoulder IR and ER strength testing at 130° abduction demonstrates strong inter-rater and intra-rater reliability.
• This novel testing position is suitable for measuring rotator cuff strength in sport-specific contexts.
• While HHD and IKD show poor to moderate concurrent validity, the HHD offers reliable measurements for clinical use.