Implications of evaluating leg muscle mass and fat mass separately for quadriceps strength in knee osteoarthritis: the SPSS-OK study.

• An increase in body mass index (BMI) up to 25 kg/m2was associated with increasing quadriceps strength. • Quadriceps strength remained almost unchanged among patients with a BMI of > 25 kg/m2. • The association between fat mass and quadriceps strength had an inverted U-shaped relationship, suggesting the importance of the separate assessment of fat mass and muscle mass in patients with knee osteoarthritis, especially those who are overweight or obese.