Reliability and Validity of Portable Muscle Measurement Device for the Assessment of Isometric Muscle Strength in the Knee of Healthy Adults

Objective: This study aimed to verify the reliability and validity of the portable knee strength measurement device IB-LS in assessing isometric knee strength in healthy adults by comparing its performance with a criterion standard dynamometer (CSMI) and exploring its potential applicability in clinical and community settings.Design: A cross-sectional methodological study employing repeated measures for test-retest reliability and criterion-referenced validation against a standard isokinetic dynamometer was conducted.Methods: Twenty-nine healthy adults in their 20s and 30s participated.Isometric knee flexion and extension strength and isokinetic strength at 60/s were measured using both the IB-LS and CSMI devices.Test-retest reliability was evaluated using intraclass correlation coefficients (ICC), and the validity between devices was assessed using Pearson correlation analysis. Results:The IB-LS demonstrated excellent test-retest reliability (ICC0.962-0.986).The concurrent validity between the IB-LS and CSMI for isometric strength was high (ICC0.799-0.895),and the correlation between the IB-LS isometric strength and CSMI isokinetic strength at 60/s was also strong (ICC0.809-0.876). Conclusions:The IB-LS is a practical, reliable, and valid tool for evaluating isometric knee strength in healthy adults.Further large-scale studies, including diverse populations and long-term follow-ups, are warranted to confirm its broader clinical applicability.These findings highlight the potential of IB-LS as a convenient alternative to laboratory-based dynamometry, which may facilitate broader applications in clinical rehabilitation and field-based assessments.