Reliability and Validity of Shoulder and Handgrip Strength Testing

Purpose: This study aimed to estimate the intra- and inter-rater reliability of the JTECH computerized, wireless apparatus and its validity (compared to established devices) for measurements of maximal shoulder isometric strength and handgrip strength among healthy adults with no shoulder pathology. Methods: Twenty healthy young adults had shoulder strength tested with JTECH and Micro-FET2 hand-held dynamometers, and the handgrip strength was tested using JTECH and Jamar handgrip dynamometers. Assessments were performed by the same rater to determine intra-rater reliability and convergent validity, at least two days apart, while on a third visit, the other rater performed measures to determine inter-rater reliability. Results: The JTECH computerized, wireless devices demonstrated good to excellent intra-rater reliability (ICCs (2,1) = 0.78-0.97) and inter-rater reliability for strength measures (ICCs (2,1) = 0.76-0.95). The JTECH computerized device compared to the Micro-FET2 hand-held dynamometer showed substantial concurrent validity for shoulder flexion (R-2 = 0.87), extension (R-2 = 0.87), abduction (R-2 = 0.88), and adduction (R-2 = 0.85). Substantial concurrent validity was shown for the JTECH computerized device and Jamar handgrip dynamometers (R-2 = 0.92). Conclusions: The JTECH computerized, wireless devices demonstrated high intra- and inter-rater reliability and substantial concurrent validity for shoulder isometric strength and handgrip strength in healthy adults.