Strength assessment in postpolio syndrome: Validity of a hand-held dynamometer in detecting change

Objectives: To investigate the validity, the intraexaminer and interexamine r reproducibility, and the ability to detect change of a hand-held dynamome ter (HHD) in strength measurements in former polio subjects. Design: HHD measurement of knee extensor strength was compared with the cri terion standard of a chair dynamometer measurement in 49 subjects. The "bre ak" method was used for HHD measurements. Reproducibility was studied for s ix lower extremity muscle groups in 28 subjects. The measurements were perf ormed by one experienced and one inexperienced examiner on two separate occ asions, with an interval of 1 week. The examiners were blinded to each othe r's and to previous results. Setting: University hospital. Subjects: Volunteer sample of former polio subjects. Results: For knee extension, the forces that could be measured with the HHD were limited to approximately 200N. Although the intraclass correlation co efficients were high (.75 to .98), the 95% limits of agreement between meas urements showed large intervals for differences between two measurements (r atio intervals ranging from .76-1.52 to .52-2.77). The intraexaminer reprod ucibility for the experienced examiner was superior to that of the inexperi enced examiner. The reproducibility of the inexperienced examiner showed sy stematic bias, with significantly higher strength values for the second ses sion measurement of three muscle groups. Conclusion: The device has good validity in the lower force range. However, because the agreement between measurements was poor, it has limited abilit y to detect a change in muscle strength. Therefore, this method is unable t o detect small changes in lower extremity muscle strength in former polio p atients. (C) 1999 by the American Congress of Rehabilitation Medicine and t he American Academy of Physical Medicine and Rehabilitation.