The intra-rater reliability of isometric shoulder muscles strength measurement in different directions of shoulder movement in healthy subjects and patients with chronic neck pain

The purpose of this study is to evaluate the intra-rater reliability of measuring isometric strength of shoulder muscles in healthy subjects and patients with neck pain. a total of 12 healthy subjects (mean age، 28. 08 ± 4. 35 years) and 12 patients with neck pain (mean age، 29. 45 ± 5. 46 years) voluntarily participated in the present study. Participants sat on a custom-made chair while they were putting their forearms on the arm rest and applying forces to the loadcell in 6 directions of the shoulder joint to reach their maximal voluntary contractions. One examiner took tests in 2 separated days 4 to 7 days apart. To assess the reliability of measuring isometric strength of shoulder muscles، ICC، SEM and SDD were assessed. The results of our study showed ICCs ranged from 0. 84 to 0. 99 in healthy subjects and ranged from 0. 66 t0 0. 95 in patients with neck pain showing high reliability of this method in both groups. The intra-rater reliability of measuring isometric strength of shoulder muscles by the custome-made chair in the present study is a highly reliable method forboth clinical and research applications.