The IDO-Isometer: a valuable alternative for measuring the strength of external rotation of the shoulder: a comparative study between two measurement devices.

Abstract

Background: The hand-held dynamometer (HHD) is widely used to assess isometric shoulder strength but may present some limitations. The present study aimed to evaluate the reliability of the IDO-Isometer as a potential alternative for measuring isometric external rotation strength of the shoulder at 90° abduction.

Methods: Ninety asymptomatic adult volunteers (45 males, 45 females) underwent strength testing of both shoulders using an HHD and the IDO-Isometer. Measurements were performed in a standardized supine position with the shoulder abducted to 90° and the elbow flexed at 90°. Each device was used three times per shoulder with a 3-minute rest interval between devices. The sequence of testing was randomized. Intra- and inter-rater reliability of the IDO-Isometer were evaluated using Intraclass Correlation Coefficients (ICCs).

Results: The IDO-Isometer demonstrated excellent agreement with the HHD, with ICC values of 0.90 (95% CI: 0.85-0.93) for both dominant and non-dominant shoulders. Intra-rater reliability yielded ICCs of 0.95 and 0.92, and inter-rater reliability showed ICCs of 0.97 and 0.96, respectively.

Conclusion: The IDO-Isometer demonstrated excellent reliability for measuring isometric external rotation at 90° shoulder abduction. Given its lower cost and ease of use, it may represent a valuable alternative to the HHD in both clinical and research settings.