Reliability and Validity of Measurements of Knee Extension Strength Obtained from Nursing Home Residents with Dementia

Objective: To describe the reliability of strength measurement by hand-held dynamometer and to identify the prediction of gait and stand-up ability by the strength measurement in people with dementia. Design: Correlational study in which 60 persons with Alzheimer disease were enrolled. The strength of knee extensor was measured twice separated by a 3-min interval using a hand-held dynamometer. The presence or absence of impaired gait and sit-to-stand was also determined. Results: Intraclass correlation coefficient was 0.97. Bland-Altman plots showed the distribution of test-retest differences in the subjects with Mini-Mental State Examination score of 10 points or fewer, increased with isometric knee extensor strength. Logistic regression analysis showed strength of the knee extensor muscles to be a significant predictor of gait performance (odds ratio, 443.0; 95% confidence interval, 9.20-21325.7) and sit-to-stand performance (odds ratio, 47.32; 95% confidence interval, 3.31-675.8). Conclusions: The strength measurement with a hand-held dynamometer was reliable in people with dementia. Furthermore, normalized knee extensor strength was indicated to be a significant predictor of gait and sit-to-stand performance. However, caution is needed when interpreting the result of strength measurement when it is carried out on subjects with a Mini-Mental State Examination score of 10 points or fewer and with a high strength level.