To investigate the public health impact of obesity and other modifiable risk factors related to physical inactivity in adults with knee osteoarthritis (OA).


The frequency of inactivity as defined by the US Department of Health and Human Services was assessed from objective accelerometer monitoring of 1,089 participants (ages 49–84 years) with radiographic knee OA during the Osteoarthritis Initiative 48-month visit (2008–2010). The relationship between modifiable factors (weight status, dietary fat, fiber, smoking, depressive symptoms, knee function, knee pain, and knee confidence) with inactivity was assessed using odds ratios (ORs) and attributable fractions (AFs), controlling for descriptive factors (age, sex, race, education, lives alone, employment, frequent knee symptoms, and comorbidity).


Almost half (48.9%) of participants with knee OA were inactive. Being overweight (OR 1.8, 95% confidence interval [95% CI] 1.2–2.5) or obese (OR 3.9, 95% CI 2.6–5.7), having inadequate dietary fiber intake (OR 1.6, 95% CI 1.2–2.2), severe knee dysfunction (OR 1.9, 95% CI 1.3–2.8), and severe pain (OR 1.7, 95% CI 1.1–2.5) were significantly related to inactivity, controlling for descriptive factors. Modifiable factors with significant average AFs were being overweight or obese (AF 23.8%, 95% CI 10.5–38.6%) and inadequate dietary fiber (AF 12.1%, 95% CI 0.1–24.5%), controlling for all factors.


Being obese or overweight, the quality of the diet, severe pain, and severe dysfunction are significantly associated with physical inactivity in adults with knee OA. All components should be considered in designing physical activity interventions that target arthritis populations with low activity levels.