Knee extension strength and body weight determine sit-to-stand independence after stroke

The sit-to-stand (STS) maneuver is important to everyday function, but independence in the activity is often lost after stroke. This study sought to determine the importance of knee extension force and body weight to independence in STS. Sixty-one primarily elderly individuals admitted for acute rehabilitation after stroke participated. Isometric knee extension force was measured bilaterally by using handheld dynamometry. Body weight and height were obtained from the medical record. The ability of subjects to rise from an armless chair without assistance was observed. Independence in the maneuver was demonstrated by 40 (65.6%) subjects when hand use was allowed and 32 (52.5%) subjects when hand use was not allowed. Univariate analysis showed that knee extension forces of the weaker and stronger sides and both sides together explained STS independence, whether hand use was allowed (R2 = 0.513–0.607) or not allowed (R2 = 0.336–0.551). Univariate analysis did not show body weight, height, gender, or age to be important; but when considered in conjunction with bilateral knee extension forces, body weight contributed to the explanation of STS independence, whether the hands were (R2 = 0.688) or were not (R2 = 0.693) used. A value of 32.1% for the combined knee extension forces of the weaker and stronger sides normalized against body weight was sensitive (87.5%) and specific (85.7%) for predicting independence in STS performed with hands. A value of 40.0% for the combined force of knee extension of the weaker and stronger sides normalized against body weight was sensitive (90.3%) and specific (86.7%) for predicting independence in STS performed without hands. Although the findings of this study do not prove cause, they suggest that efforts to foster independence in STS after stroke should focus on strengthening both lower limbs. For individuals who are overweight or obese, weight loss may also help.