Hand Size Reduces the Reliability of K-Force® Grip Dynamometer

Background: Objective evaluation of grip strength is crucial for determining functional status of patients and demonstrating treatment effectiveness. A novel dynamometer, K-Force® Grip, has been developed that can work in conjunction with smart devices. However, the device has a smaller circumference compared to the Jamar®Plus+ and lacks an adjustable grip width, unlike the Jamar®Plus+. The aim of this study was to assess the validity and reliability of the K-Force® Grip across different hand sizes in healthy subjects. Methods: We recruited 1 23 healthy subjects (n=246 hands) and categorized them based on hand length and span. Grip strength was measured using both the Jamar®Plus + hydraulic hand dynamometer and the K-Force® Grip dynamometer. Results: Inter-device consistency was excellent for the overall population (ICC=0.937) and for individuals with large hand spans and long hand lengths. It was good for other anthropometric groups. However, ICC estimates for absolute inter-device agreement indicated high variability and were unstable (as indicated by the confidence intervals including zero). BlandAltman plots suggest K-Force® values are systematically lower than those from the Jamar®Plus+. Conclusion: The devices should not be used interchangeably in research settings. For clinical follow-up, the Jamar®Plus + dynamometer is recommended, especially in adolescent populations where hand growth continues over time.