The Reliability and Validity of an Isometric Knee Strength Measurement Device in Older Adult Individuals

This study aims to evaluate the reliability and validity of the Leg Strength Analyzer (IB-LS) in assessing isometric knee flexion and extension strength in elderly adults, compare its performance with that of the CSMI dynamometer, and examine its agreement with isokinetic knee strength measurements. A total of 21 elderly participants (mean age: 65.10 ± 4.56 years) were recruited. Participants underwent knee flexion and extension strength assessments using both the IB-LS and CSMI devices, with isokinetic strength at 60°/s measured in a follow-up session at least one day later. The IB-LS demonstrated high test-retest reliability in elderly adults (ICC = 0.856-0.987). The validity analysis comparing IB-LS isometric peak torque with CSMI isometric peak torque showed moderate to high validity (ICC = 0.826-0.946). Furthermore, IB-LS isometric peak torque and CSMI isokinetic 60°/s peak torque demonstrated high agreement (ICC = 0.775-0.881), demonstrating its strong association with isokinetic strength assessments. Bland-Altman analysis revealed that mean differences between IB-LS and CSMI isometric peak torque values ranged from 13.2 to 93.5 Nm, with limits of agreement (LoA) spanning from -55.8 to 192.5 Nm. When comparing IB-LS isometric peak torque with CSMI isokinetic 60°/s peak torque, mean differences ranged from 31.0 to 56.0 Nm, with LoA from -28.5 to 138.9 Nm. The IB-LS is a reliable and valid tool for evaluating isometric knee strength in elderly adults. Its strong agreement with the CSMI dynamometer and close correlation with isokinetic strength measurements indicate that IB-LS can be a feasible alternative for assessing knee strength in clinical and research settings focused on elderly populations.