Intrarater and interrater reliability of three isometric dynamometers in assessing shoulder strength

The purpose of this study was to evaluate the reliability of three separate isometric strength testing devices. Seventeen (10 female, 7 male) adult volunteers with no known shoulder dysfunction participated. Each subject's internal rotation, external rotation and abduction strength was measured with the Nicholas Manual Muscle Tester (MMT), Biodex Isokinetic Dynamometer, and Isobex 2.0. Two investigators administered the test to each subject with each device. Data were analyzed with intraclass correlation coefficients (ICCs). Ranges of the intrarater intraclass correlation coefficient (3,1) values for each muscle group with each device for both testers were as follows: Nicholas MMT = .84 to .97, Biodex = .97 to .99, and Isobex 2.0 = .95 to .98. Ranges of interrater intraclass correlation coefficient values for each device and muscle group were as follows: Nicholas MMT = .79 to .94, Biodex = .93 to .96, and Isobex 2.0 = .90 to .97. Time to complete testing was shortest for Nicholas MMT, followed by Isobex 2.0, then Biodex. Measurements taken on the same day by the same therapist appear to be highly reliable for all three devices. Measurements taken over a 3-day period by two therapists appear to be highly reliable for all devices and muscle groups with the exception of Nicholas MMT abduction (.79), which was moderately reliable.