Relative and Absolute Reliability of the Knee Extensor Muscle Strength of Healthy Subjects

Abstract

[Purpose] The purpose of this study was to assess the relative and absolute reliability of knee extensor muscle strength measurements of healthy young persons. [Participants and Methods] The participants were 9 healthy young men. Measurement of knee extensor muscle strength was performed using a Locomoscan® which can assess the long sitting position. Measurements of the right side lower limb were performed twice. The test-retest reliability was estimated using the intra-class correlation coefficient [ICC (1,1)] and Bland-Altman analysis. [Results] The mean knee extensor muscle strength of the first measurement was 0.81 ± 0.18 N/kg, and 0.83 ± 0.10 N/kg for the second. The relative reliability was substantial, ICC (1,1)=0.68. Bland-Altman analysis found a proportional bias, a systematic error, in the absolute reliability. [Conclusion] Although the relative reliability was substantial, absolute reliability was not guaranteed. We consider that a systematic error was introduced by the experimental procedure, either through reproduction of the measurement position or number of determinations.