Intra- and inter-instrument reliability of Grip-Strength Measurements: GripTrack™ and Jamar® hand dynamometers

Abstract

The purpose of this research was to compare the computer-connected GripTrack dynamometer and the manual Jamar dynamometer to determine the intra- and inter-instrument reliability. Using a repeated-measures design the instruments were calibrated three times. Forty-six uninjured female health workers (mean age 29.7 years) performed three consecutive grip strength trials per hand and per instrument with the handle bar in the second position, alternating which dynamometer was used first.Intra-instrument reliability and concurrent validity were tested using certified standard weights. Both the Jamar dynamometer and GripTrack dynamometer demonstrated concurrent validity with certified standard weights (Jamar r = 1.0, GripTrack dynamometer r ≥ 0.9994). While inter-instrument reliability was good, starting with the Jamar dynamometer as the first instrument (ICC 0.80 to 0.83), and excellent, starting with the GripTrack dynamometer (ICC 0.94 to 0.95), the Bland and Altman method of analysing the differences between the two instruments’ grip strength readings revealed instrument bias. The large spread of limits of agreement from –2.37 kg to 7.87 kg (± 2 SD from the mean 2.75 kg) suggests variation in readings of up to 10.24 kg.While both dynamometers retain adequate calibration, the human interfaces are sufficiently different to cause large differences in readings between the dynamometers, making them non-interchangeable.