Test-retest reliability of the biodex system 4 isokinetic dynamometer for knee strength assessment in paediatric populations

Background: Isokinetic dynamometry is a widely used tool for measuring muscle strength in clinical intervention and rehabilitation as well as research in children. Objective: To assess the test-retest reliability of knee flexor/extensor strength using the Biodex Multi-Joint System 4 Isokinetic Dynamometer in children. Methods: Peak isometric knee extensor (KE) and peak isokinetic knee flexor (KF) torques of the dominant and nondominant limbs were assessed twice in 11 children aged 10 to 13 yrs, 7 to 10 days apart. Results: Peak torques were higher in the dominant limb (p ≤ 0.006). Peak isometric KE torque was 8.4% higher (SEM 2.5%) at the second testing session, but there was no interaction with the limb tested (p > 0.2). Peak isokinetic KE/KF torque ratios agreed well between tests and had intraclass correlation coefficients (ICCs) of 0.96. Conclusions: The dynamometer provides a reliable means of assessing knee strength in 10 to 13 year olds, with excellent testretest reliability for isokinetic KE/KF. A learning effect occurred when assessing isometric torque, indicating the importance of habituation for this measure.