Reliability of measurements of hip abduction strength obtained with a hand-held dynamometer

This study aimed to evaluate intrarater and interrater reliability when measuring hip abductor strength in the supine position using a hand-held dynamometer (HHD) (Study 1), and to elucidate the relationships between measured values and examiners' physical characteristics (Study 2). Three healthy examiners (1 female, 24 y.o. and 2 males 23 and 27 y.o) and 12 subjects (6 females, 24.5 +/- 2.8 years and 6 males, 27.7 +/- 3.5 years) participated in Study 1, and 20 healthy examiners (7 females, 22.3 +/- 1.3 years and 13 males, 29.4 +/- 8.2 years) and 2 subjects (1 female, 24 y.o. and 1 male 27 y.o) participated in Study 2. All healthy examiners were hospital employees. Hip abductor strength was measured by HHD with hand fixation and with belt fixation, and examiner age, sex, height, weight, BMI, and dominant hand grip strength were evaluated. The intraclass correlation coefficient (ICC) (1,1), a measure of intrarater reliability, was 0.89-0.95 with hand fixation and 0.96-0.97 with belt fixation. ICC (2,1), a measure of interrater reliability, was 0.76-0.79 and 0.90-0.93, respectively. In subjects with high muscle strength (the examiner's hand was moved), the examiner's dominant hand grip strength affected muscle strength values with hand fixation (standardized partial regression coefficient = 0.78, determination coefficient R-2 = 0.61, p<0.01). In subjects with low muscle strength (the examiner's hand was not moved), no variables had effect. When the muscle strength of the subject is weak, both methods can be used. When the muscle strength of the subject is strong, it is necessary to adjust the value obtained by the examiner's dominant hand grip strength in the hand fixation method.