People who are obese have a significantly increased risk of developing arthritis, because obesity is an important source of chronic microtrauma to the cartilage. Joints are designed for carrying, properly distributing, and cushioning body weight. They are also capable of taking on temporary excess loads. For example, stress on the joints is greatly increased when we carry groceries, lift weights, bend over, or run up stairs. However, joints do have limits.
Each step you take while walking involves temporarily transferring your weight primarily onto one joint. When you factor in momentum, biomechanics, and gravity, your knees and hips experience up to three times as much pressure as your body weight with each step. If you weigh 140 pounds, your knee joints may experience as much as 320 pounds of weight with each step. When you walk down a flight of stairs, your hip and knee joints may experience as much as a six-fold increase in weight, so that same 140-pound person experiences as much as 640 pounds across the knees and hips.
In other words, every pound you gain punishes your joints up to six-fold. Research clearly bears this out; overweight men are five times more likely to develop arthritis, and overweight women are four times more likely to develop it than are their non-overweight counterparts. For every 10 pounds of excess weight gain, the risk of developing arthritis increases by 40 percent. Every time you take a step, the extra weight places increased pressure on your weight-bearing joints, because the load is too great for your muscles, ligaments, and tendons. The joints shift under the weight and, ultimately, they are overwhelmed, resulting in repetitive microtears in the cartilage. Additional stresses are taken up by static portions of your bone, creating friction. Your bone responds by trying to build new bone, but the new bone is weaker than the original bone, and the process of arthritis is well on its way.
