Test-retest reliability of isometric shoulder muscle strength measurement with a handheld dynamometer and belt

[Purpose] The aim of this study was to develop a method of measuring isometric shoulder joint muscle strength using a handheld dynamometer with a belt and investigate its test-retest reliability. [Subjects] The subjects comprised 40 healthy adults. [Methods] Six types of isometric shoulder muscle strength were measured twice, and reliability was assessed. [Results] The intraclass correlation coefficient (1, 1) values ranged from 0.976 to 0.902. The result of a Bland-Altman analysis showed differences in the types of errors between measurement items. [Conclusion] The relative reliability of isometric shoulder muscle measurement using a handheld dynamometer with a belt was high. However, analysis of absolute reliability revealed errors that may affect interpretation of values; therefore, it was considered that adapting the greater of two measurement values is appropriate.