HAND-HELD DYNAMOMETER POSITIONING IMPACTS DISCOMFORT DURING QUADRICEPS STRENGTH TESTING: A VALIDITY AND RELIABILITY STUDY

Purpose/Background: A belt-stabilized hand-held dynamometer (HHD) offers the ability to quantify quadriceps muscle strength in a clinical environment, but a limitation is participant discomfort at the interface between the HHD and the tibia. The purpose of this study was to quantify the level of discomfort associated with a modified belt-stabilized HHD configuration compared to a standard belt-stabilized configuration and an isokinetic dynamometer. The secondary purpose of this study was to determine the validity and reliability of a modified configuration used to measure quadriceps strength compared to the "gold-standard" isokinetic dynamometer. Methods: Twenty healthy participants (5 males, 15 females; age = 24.7 +/- 2.2 years, height = 171.1 +/- 8.8 cm, mass = 72.0 +/- 18.7 kg) performed maximal knee extension isometric contractions during each of three testing conditions: isokinetic dynamometer, standard configuration with HHD placement on the tibia, and an alternative configuration with the HHD interfaced with the leg of a table. Discomfort was quantified using a Visual Analog Scale (VAS). Differences in discomfort and torque (N.m) associated with the testing positions were determined using Friedman test or repeated measures analysis of variance. Validity was quantified using Pearson correlations and within-session intrarater reliability was determined using an intraclass correlation coefficient (ICC2,1) and associated confidence intervals (95% CI). Results: The isokinetic dynamometer configuration resulted in the least discomfort (p < .01) and the modified configuration was more comfortable than the standard configuration (p = .003). There was a significant correlation between measures from the isokinetic dynamometer and the standard configuration (r = .87) and modified configuration (r = .93). Within-session intrarater reliability was good for both the standard configuration (ICC2,1 = 0.93) and modified configuration (ICC2,1 = 0.93) conditions. Conclusions: The use of the modified belt-stabilized HHD configuration, where the HHD was interfaced with the leg of a table, offers a more comfortable alternative compared to the standard belt-stabilized configuration to obtain isometric quadriceps strength measures in a clinical environment. This configuration is also a valid and reliable alternative to the "gold-standard" isokinetic dynamometer when testing isometric quadriceps strength at 90 degrees of knee flexion.