Knee extensor strength measured using a Biodex dynamometer and an adapted hand held dynamometer

Abstract

Background: Muscle strength is widely used as an outcome measure in rehabilitation and knee extensor strength is an important determinant of physical function. Hand held dynamometry (HHD) is portable and easy to use; however, reliability of HHD measurements is significantly influenced by the strength of the tester. The present study assessed the agreement between an adapted HHD and Biodex dynamometry while measuring knee extensor strength in young adults. Method: Thirty participants aged 22–35 years (mean age 24.4 years; SD ± 2.5) were studied. Peak isometric knee extensor strength of the dominant leg was measured using the Biodex dynamometer and adapted HHD. The agreement between the maximum voluntary contractions (MVC) was analysed using Pearson's Correlation Coefficient, intraclass correlation (ICC) and Bland–Altman analysis. Results: The mean peak knee extensor MVC was 191.7 Nm (± 53.6) for the Biodex dynamometer and 167.5 Nm (± 55) for the adapted HHD. The mean difference in peak knee extensor strength measured using the adapted HHD was 24.1 Nm (± 30.3) lower when compared to the Biodex. However, there was good correlation between the two measures (r=0.796, ICC (3, 1): peak torque=0.796; average of three trials=0.808) and Bland–Altman plots confirmed good agreement. Conclusions: The knee strength measurements were not influenced by examiner strength and results obtained using the adapted HDD were comparable to that using the Biodex; however, the absolute knee extensor strength obtained using the adapted HHD was generally lower.