Comparison of portable handheld versus fixed isokinetic dynamometers in measuring strength of the wrist and forearm

Purpose: The purpose of this study was to test the concurrent validity of using hydraulic dynamometers in comparison to the gold standard isokinetic dynamometers in measuring wrist and forearm strength. Materials and methods: Healthy adults between the ages of 18-65 participated, including 24 participants, 8 men and 16 women. The examiner used a handheld dynamometer, forearm/wrist dynamometer, and an isokinetic dynamometer to measure force/torque production in forearm rotation and wrist flexion/extension using a standardized protocol of two handle types for each motion. Sequence of testing was randomized. The data were analyzed using Pearson correlation coefficients and paired t-tests. Results: When matched for handle type, three of the four correlations between the strength measurements taken with the different dynamometers were moderate to high with Pearson product moment coefficients ranging from 0.72 to 0.96; the screwdriver handle demonstrated less than acceptable correlation (r = 0.45, 0.67 for wrist flexion and extension, respectively). There were significant differences in most of the force/torque values obtained by different handle types for wrist and forearm motions. Discussion and conclusions: Overall, the dynamometers demonstrated acceptable correlations supporting concurrent validity for measuring forearm and wrist strength, except with the screwdriver handle. However, different tools, positions, and handle interfaces provided different absolute values, therefore the tools cannot be used interchangeably. It is recommended that repeated measurements to monitor patient progress are taken with the same tool and handle type.