What role does obesity play in knee pain?

Carrying extra weight is directly related to knee pain. One review article found that obesity (defined as having a body mass index of 30 or above) leads to pain, limits activity, and increases the risk of needing a total knee replacement. Another study of 5,700 Americans over age 60 showed that the more obese a person was, the more likely he or she was to experience knee pain. About 56% of severely obese people had significant knee pain, compared with 15% of people who were not overweight.

Such findings are not surprising when you consider that with each step on level ground, you put one to one-and-a-half times your body weight on each knee. So a 200-pound person can put 300 pounds of pressure on each knee with each step. The burden is even higher when you go up and down stairs (two or three times as much weight) or squat (four or five times). So if you're 50 pounds overweight, the simple act of going downstairs and squatting to move clothes from the washer to the dryer puts hundreds of extra pounds of force repetitively on your knees.