Comparison of three hand dynamometers in relation to the accuracy and precision of the measurements

Background: Given the variety of available hand-held dynamometers and their different handle shapes, reliability studies are needed. Objectives: To compare the accuracy and reliability between three different hand-held dynamometers and analyze the influence of their handles on grip strength. Methods: The tests were performed with the Jamar (R) dynamometer, the Takei (R) dynamometer and the EMG System Manual Transducer with modified handle. Eighteen healthy volunteers aged 20.0 +/- 1.3 years without history of musculoskeletal disorders or trauma in the evaluated limbs were included. Data normality was tested using the Shapiro-Wilk test. To verify possible differences between the dynamometers, repeated measures ANOVA was administered, followed by Tukey post-hoc tests. Reliability between measurements was evaluated using intraclass correlation coefficient (ICC) and agreement was tested using Bland and Altman plots. The dynamometers calibration process was evaluated using linear regressions. Results: We observed statistically significant differences on the female group between the Jamar (R) and the Takei (R) dynamometers (females p<0.001 and males p=0.022) and the EMG System Manual Transducer (female p<0.001 and males p=0.007). However, the Takei (R) dymamometer and the EMG System Manual Transducer were similar for both female (p=0.161) and male groups (p=0.850). Although acceptable values of intraclass correlation coefficients between measurements were identified, low agreement between the Jamar (R) dynamometer and all other instruments was found. Conclusions: The results demonstrated that there is an influence of the dynamometer's handle shapes on the measurements of grip strength. Furthermore, the results demonstrated the need for previous calibration of this type of instrument.