Relationship of knee extension force to independence in sit-to-stand performance in patients receiving acute rehabilitation.

BACKGROUND AND PURPOSE The ability to rise from a chair is important for independence in everyday life. This study was conducted to determine to what extent knee extension force (KEF) could explain independence in sit-to-stand (STS) performance from a standard chair. SUBJECTS AND METHODS This was a descriptive and correlational study of patients receiving acute rehabilitation (N=107). Measurements of KEF of both lower extremities were obtained using manual muscle testing (MMT) and hand-held dynamometers (HHDs). The HHD measurements were normalized based on body weight and age- and sex-specific reference values. Measurements of the ability to stand without using the upper extremities (STS [without hands]) and to stand using the upper extremities (STS [with hands]) were correlated with the force measurements. RESULTS The correlations (r) of the KEF measurements with STS success ranged from.652 to.708 for STS (without hands) and from.545 to.638 for STS (with hands). Body weight added to the explanation of STS (without hands) (R=.662) and STS (with hands) (R=.584) provided by KEF measured by HHD. The receiver operating characteristic curves showed that HHD (weight normalized) was the most sensitive and specific measure for explaining independence in STS. DISCUSSION AND CONCLUSION Manual and dynamometric measurements of KEF are related to independence in STS. Measurements of KEF quantified with a dynamometer and normalized against body weight provided the most valid, specific, and sensitive cutoff point for explaining STS independence.