Alternatives for measuring knee extension strength of the elderly at home

Objective: To examine the construct validity of three measures of knee extension strength obtained from elderly individuals. Design: Retrospective and cross-sectional. Setting: Home care. Subjects: Forty-one consecutively treated patients (mean age 79.2 years). Measures: Knee extension strength was measured using manual muscle testing, hand-held dynamometry, and the sit-to-stand test. Results: Convergent construct validity was supported by the significant correlations between the measures (r s = 0.578–0.702). Discriminant construct validity was confirmed by the finding of significant differences in the manual muscle test scores and in the hand-held dynamometer measures of patients who were unable versus able to stand from a chair without the upper extremities or help. The sensitivity of the two measures for discriminating between patients able versus unable to stand from a chair was 90.9% for manual testing and 68.2% for dynamometry. The specificity was 78.9% for manual testing and 94.7% for dynamometry. Conclusion: The results of this study show that the three measures employed to characterize knee extension strength are valid when employed with elderly patients in a home care setting.