Comparative study on the assessment of the strength of the knee extensor and flexor muscles by hand-held dynamometer and isokinetic dynamometer

Abstract

The strength of the knee extensor and flexor muscles is a relevant clinical indicator of the health status and functional capacities of an individual. For its evaluation, the practitioner must have simple and reliable measuring tools. Currently, the use of hand-held dynamometers is widespread both in the clinical practice and in research. However, their reliability for assessing the performance of strong muscles, such as the knee extensors and flexors, needs to be fully validated. The aim of this study is to compare the knee extensor and flexor muscle strength measurements using a hand-held dynamometer and the “gold standard” isokinetic dynamometer in a population of healthy individuals. The strength of the knee extensors and flexors was measured in 30 volunteers with a hand-held dynamometer (MicroFet 2, Hogan Health Industries, Inc 8020 South 1300 West, West Jordan, USA) and with an isokinetic dynamometer (Con-Trex MJ, CMV AG, Dübendorf, Switzerland). The correlations between the mean values of maximal isometric voluntary contraction measured with the hand-held dynamometer and the peak torque values in concentric, eccentric and isometric testing mode were then analyzed. Cross-sectional study. The reproducibility of the hand-held dynamometer was very good with coefficients of variation ranging from 3.2% (95%CI, 2.6–3.8%) to 4.2% (95% CI, 3.5–4.9%) depending on the muscle group. Strong positive correlations were found between hand-held and the isokinetic dynamometers. The correlation coefficients ( r ) ranged from 0.715 (95% CI, 0.478–0.855) to 0.872 (95% CI, 0.747–0.938) according to the muscle group and the isokinetic evaluation mode ( P < 0.01). The force values of the knee extensor and flexor muscles recorded with the hand-held dynamometer are reproducible and strongly and positively correlated with the values obtained with the three isokinetic evaluation modes, indicating that hand-held dynamometry represents a potential alternative tool for knee muscle strength assessment.