Validity of Lower-Extremity Strength Between Push- and Pull-Based Handheld Dynamometers: A Technical Report

Handheld dynamometers provide clinicians an objective measure of lower-extremity force production at the hip and knee. While push-based dynamometers are common in clinical practice, they can be associated with patient discomfort, and standardization of methods is challenging when patient forces can exceed the ability of the rater. Development of novel, pull-based dynamometers allow for better patient comfort, but validity between dynamometers must be established before integration into clinical practice. Therefore, the purpose of this study was to compare measurement of lower-extremity force between push- and pull-based handheld dynamometers.

Descriptive laboratory study.

Twenty-one healthy triathletes performed isometric hip abduction, hip external rotation, and knee extension testing against 2 separate handheld dynamometers. Pearson product correlations were calculated for the relationship between devices, while Bland-Altman plots were used to measure agreement with limit of agreement to assess systematic bias.

Correlations between devices were strong for hip abduction and knee extension (r = .743-.767, P < .001) and moderate for hip external rotation (r = .429, P = .052). Additionally, there was good agreement between the 2 devices, with acceptable limits of agreement across the 3 force tasks. The pull-based dynamometer resulted in greater torque values for knee-extension and hip external rotation, with a mean difference of -0.37 and -0.19 N·m/kg, but there was no difference in hip abduction with a mean difference of 0.03 N·m/kg.

The results demonstrate that pull-based dynamometers are an acceptable alternative to push-based dynamometers for hip abduction and knee extension, but some caution may exist for hip external rotation. Clinicians should be aware of differences in lower-extremity force across multiple handheld dynamometers when assessing muscle function in practice.