Reliability and validity of the Grip-Ball dynamometer for grip-strength measurement

Grip-strength measurement is a key element in the evaluation of numerous conditions including frailty. An innovative grip-strength evaluation tool, the Grip-Ball has been developed for remote assessment of grip-strength. The Grip-Ball is an airtight ball that can be inflated to different pressures, thus varying the stiffness of the ball and the grip-strength dynamics. Three different initial pressures of 100, 125, and 150 kPa were evaluated in respect to reliability and validity, when compared to the Jamar. Reliability was very high, with ICC values of 0.95, 0.98, and 0.99 for 100, 125, and 150 kPa, respectively. The new device was highly correlated with the force measured using the Jamar for all initial pressures (r = 0.88, 0.93, and 0.93 for 100, 125, and 150 kPa, respectively). The possibility of varying the initial pressure would enable the Grip-Ball to be used for standard grip-strength testing and rehabilitation, while still maintaining high reliability and validity.