Testing of knee extension muscle strength: A comparison of two portable alternatives for the NIH toolbox study

Abstract

Given the functional and epidemiological significance of lower extremity strength, portable, low-cost measures of lower extremity strength with robust psychometric properties are needed for clinical practice and research. The purpose of this study was to compare measures of isometric knee extension strength obtained with portable devices with criterion measures obtained with a Biodex dynamometer. Sixty-eight healthy adults from Illinois and Connecticut participated in this study. Each participant's isometric knee extension strength was tested in random order using: 1) an integrated tension load cell device (ITLCD), 2) a belt stabilized hand held dynamometer (BSHHD) and 3) a Biodex System 3 isokinetic dynamometer. Equivalence of the 3 measures was evaluated using repeated measures analysis of variance (ANOVA), Pearson correlations (r), and intraclass correlation coefficients (ICCs). Results supported good agreement between measures obtained with the ITLCD, BSHHD and Biodex ( r> 0.90, ICCs > 0.79). The ANOVA results demonstrated that measures obtained with the ITLCD and the BSHHD did not differ significantly. On average, the maximum isometric knee extension torque was underestimated by 27 N-m and 32 N-m by the ITLCD and BSHHD, respectively. Because The ITLCD was slightly better at approximating Biodex torque scores and does not depend on skills of the examiner, the ITLCD was recommended for inclusion in the motor battery of the NIH Toolbox.