Hand-held Dynamometer Measurements: Tester Strength Makes a Difference.

Three examiners with measurably different strengths and three muscle groups with distinctly different maximum force productions were used to investigate the effect of tester strength on the magnitude and reliability of hand-held dynamometer (HHD) force measurements. Each examiner measured the shoulder external rotator, elbow flexor, and knee extensor muscles of 27 healthy adults twice during two sessions (one week apart). Intrarater/intrasession, intrarater/intersession, and interrater/intrasession reliability coefficients (ICCs) were calculated. Interrater ICCs decreased in magnitude (.932 to .226) as the tested muscle groups increased in force production. Intrarater/intersession ICCs indicated a similar trend. High intrarater/intrasession and interrater/intrasession ICCs calculated from shoulder external rotator measurements indicated that HHD testing for muscle groups generating a mean maximum force of about 120 N may be reliable for clinicians with strengths equal to or exceeding those of the weakest tester in this study. Above 120 N, tester strength appeared to be a major determinant of the magnitude and reliability of the forces measured with a HHD. Further investigation into the relationship between tester strength and the intrarater and interrater reliability of HHD measurements is warranted. J Orthop Sports Phys Ther 1991;13(4):191-198.