Body Weight-Normalized Knee Extension Strength Explains Sit-to-Stand Independence: A Validation Study

Abstract

The purpose of this study was to validate the ability of body weight-normalized knee extension strength to explain sit-to-stand (STS) independence in home care patients. Isometric knee extension force of 31 seated patients (mean age 72.8 years) was measured with a handheld dynamometer. The combined force of both knees was then normalized against body weight. The patients' ability to stand from a chair without using their upper limbs was observed. Independence in the task was correlated significantly (rpb = 0.711, p < 0.001) with strength. Regression analysis revealed a positive odds ratio for strength as a predictor of STS independence (1.197, 1.055-1.357). Receiver operating characteristic analysis showed an area under the curve of 93.7%. The normalized strength cutoff point of 46.3% provided the best sensitivity (85.7%) and specificity (88.2%). This study supports previous research showing a strong relationship between normalized knee extension strength and STS independence. The cutoff points of this and previous studies can serve as goals for muscle strengthening for individuals unable to stand from a chair without use of their upper limbs.