Obesity. The relationship among obesity, joint pain, functional impairment, and physical activity levels is complex. Obesity, which now affects 33.8% of adults ages 20 years and older in the United States, is a significant risk factor for the development and progression of OA, especially in the knee but also in other joints.12 The increased load that obesity places on joints can exacerbate the pain and functional limitations of OA.4, 13 Because of the physics of knee movement, activity magnifies the load across the knee from upper-body weight by three to seven times. Therefore, weight loss in obese patients, especially if accompanied by increased physical activity, can improve physical function and quality of life.14