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 (rs = 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.