One of my professors in PT school once said that if you live long enough, you’ll get osteoarthritis (OA).
I asked him why and he said, “You get one dose of cartilage and you’ll just wear it out over time. No blood supply. No metabolism. Simple as that.”
If he’s right, then sitting around is the way to go. Spare your joints and they’ll last longer.
But there’s something interesting going on now. The prevalence of osteoarthritis has almost doubled since the mid-20th century. And, our society has become more sedentary. Nearly 80% of adults in the US fail to meet the The Center for Disease Control’s national fitness guidelines.
Sitting around won’t save you from OA.
You may have heard that old adage, “use it or lose it”. Neuroscientists use it to describe how the brain changes when learning new skills. You can also say the same thing about the body.
Up to a point, that is.
Maintaining a healthy joint, like the knee joint for example, requires a couple of things.
One is motion.
My professor was correct that articular cartilage has no blood supply. But he was wrong about it not having a metabolism.
Articular cartilage has two main sources of nutrient supply. One is from the synovial fluid in the joint space and the other is from the bone underneath the cartilage.
So, when you move your knee, you swish the fluid around in the joint bathing the joint surface. In a sense, you’re feeding it.
The second thing needed is load.
And this is where it gets tricky.
Cartilage cells need a certain amount of external force to stay healthy. This is why weight bearing exercise is important for you.
But, too much force at one time, or a little too much force over an extended period of time can cause the tissue to breakdown.
You have good intentions. You want to shed some extra weight and get in better shape.
But, your joints aren’t prepared for the force from jogging (several times your body weight). This sudden change will be too much too soon. If you continue down this path, your joints may start to ache or swell.
Joint are nudged into health, not pushed. You have to give the joint time to adapt. And the good news is, if you’re patient, your body will change. Your joints will get healthier, stronger.
When it comes to “use it or lose it”, joints have a unique feature, different than the brain.
For joints, the phrase is “use it wisely or lose it”.
 Wallace, I. J., Worthington, S., Felson, D. T., Jurmain, R. D., Wren, K. T., Maijanen, H., . . . Lieberman, D. E. (2017). Knee osteoarthritis has doubled in prevalence since the mid-20th century. Proceedings of the National Academy of Sciences, 114(35), 9332-9336. doi:10.1073/pnas.1703856114
 I.F. Petersson, T. Boegard, B. Svensson, D.Heinegard, T. Saxne Changes in cartilage and bone metabolism identified by serum markers in early osteoarthritis of the knee joint. Br J Rheumatol, 37 (1) (1998), pp. 46-50
 Leong, D. J., Hardin, J. A., Cobelli, N. J., & Sun, H. B. (2011). Mechanotransduction and cartilage integrity. Ann N Y Acad Sci, 1240, 32-37. doi:10.1111/j.1749-6632.2011.06301.x