Reliability and measurement error of hip abductor muscle strength using a hand-held dynamometer in healthy adults

[Purpose] Patients with hip osteoarthritis commonly exhibit weakened hip abductor (HA) muscles. Accurate assessment of muscle strength is critical; however, the reliability of HA strength measurements remains underreported. This study aimed to evaluate reliability and measurement error for HA muscle strength values measured with a hand-held dynamometer (HHD). [Participants and Methods] Two physical therapists measured HA muscle strength in 20 healthy adults (40 limbs) using an HHD. Participants were positioned supine, with lower limbs placed in a belt loop. Average and maximum values from the two trials were used for analysis. Reliability was assessed using intra-class correlation coefficients (ICCs). To evaluate changes in HA muscle strength, the minimal detectable change (MDC) of normalized strength values was calculated using an equation. [Results] Inter-rater reliability was excellent, with ICCs of 0.95 and 0.92 for average and maximum values, respectively. The associated standard errors of measurement and MDC values were 1.65 and 8.1 for average values, and 2.25 and 10.9 for maximum values, respectively. [Conclusion] Measuring hip abductor muscle strength using an HHD demonstrated excellent reliability. Using average value effectively reduced inter-rater variability and improved reliability.