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How obesity breaks your body down joint by joint

How obesity breaks your body down joint by joint

Picture of William Heisel
Photo: Getty Images
Photo: Getty Images

If you have ever bought a used car, you know that you don’t want your car to bounce too much when it hits a bump.

If it does, it means the struts are worn out from too much use and too much weight bearing down on them over time.

One of the ways obesity leads to more arthritis in the population is the way it works on the joints, much like the way your car and everything you load into it works on those struts.

In medical terms, physicians and researchers talk about “excessive joint loading” leading to things like articular cartilage degradation, osteophyte formation, synovitis, and subchondral bone sclerosis.

Because these are the most obvious manifestations of obesity’s effect on the musculoskeletal system, let’s take those first. We’ll explore the less understood ways obesity leads to arthritis in later posts.

The first thing to understand is that there’s weight and then there’s the force of your movements. Both things are in play creating problems with joints. That’s why studies have shown that an increase in weight doesn’t just lead to an equal increase in pressure on the joints. It leads to as much as five times the pressure. Here’s how Harvard Medical School describes it:

When you walk across level ground, the force on your knees is the equivalent of 1½ times your body weight. That means a 200-pound man will put 300 pounds of pressure on his knees with each step. Add an incline, and the pressure is even greater: the force on each knee is two to three times your body weight when you go up and down stairs, and four to five times your body weight when you squat to tie a shoelace or pick up an item you dropped.

All that pressure breaks down the cartilage in the knees, hips and other joints. It begins with what physicians sometimes refer to as “repeated microtrauma” to the cartilage cells, small injuries that lead to big damage over time. When these repeated injuries create inflammation, that can create stiffness and loss of movement. The injuries also can lead to tears or cracks in the cartilage. When that happens, new cells that make up the cartilage – known as chondrocytes for you musculoskeletal junkies out there – are created to fill in the cracks.

“Unfortunately, this new tissue is inferior to normal cartilage, and it is more likely to crack and overgrow into places where it’s not needed, interfering with normal functioning,” writes Grant Cooper in “The Arthritis Handbook.”

Here’s the good news. Even once you have developed arthritis, weight loss works to reduce the stress on your joints. Multiple studies have shown this effect. Jennifer Warner wrote in WebMD about a 2005 study that showed how even small amounts of weight loss had significant benefits. Dr. Stephen Messier of Wake Forest University told her:

The accumulated reduction in knee load for a 1-pound loss in weight would be more than 4,800 pounds per mile walked. … For people losing 10 pounds, each knee would be subjected to 48,000 pounds less in compressive load per mile walked.

That’s what happens to the joints that are carrying all the extra weight. But what about non-weight bearing joints?

More and more research is showing that weight on the joints is just part of the problem. I will explore some of the other links between obesity and arthritis in my next post.

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