Your knee joint is a synovial joint which consists of a synovial membrane that surrounds the joint allowing your knee to be bathed in synovial fluid. Synovial fluid plays three main rolls for your knee joint:
- reduces friction
- absorbs shock
- supplies nutrients and carries away waste products
The bony surfaces inside your knee joint are covered with hyaline cartilage which ensures smooth movement by decreasing friction and fibrous cartilage (the meniscus) which helps deepen the tibial sockets and play a role in shock absorption.
Knee injuries including cartilage tears (meniscus tears) and damage (arthritis) are common and often blamed on "wear and tear over time." Basically people are saying your knee will wear out like your car tires after so many miles. There is a major flaw with this line of thinking because the last time I looked my car tires are made up of rubber (i.e. a non-living substance) and my knees are made of many types of cells (all living). Living cells grow, divide, die and respond to their environment like all living things and the cells inside our knees are no different.
Let's say you decide to start lifting weights several times a week for the next year. Then we compare your muscles of today with your muscles of next year, what changed? They are bigger! Why? Because they are responded in a positive way to the stimulus given to them, it's what our bodies do naturally and automatically.
Let's say instead of lifting weights you decided to start running several times a week for the next year. Then we compare your knee cartilage of today with your cartilage of next year, what changed?
Many people will say knees are damaged from the "pounding" and "wear and tear" and if you keep up your running eventually you'll end up with arthritic knees and probably need a knee replacement. But science is starting to tell us otherwise and has shown that runners have healthier knees (than non-runners), long distance running does not damage knees, running conditions the cartilage for load, and running decreases the incidence of knee arthritis.
"Without exercise, cartilage cells get weak and sick, making them susceptible to injury.“
- James Fries, M.D., professor of medicine at Stanford University School of Medicine
In fact, Dr. Miller said, the study’s results intimate that running potentially could be beneficial against arthritis.
“There’s some evidence” from earlier studies “that cartilage likes cyclical loading,” he said, meaning activity in which force is applied to the joint, removed and then applied again. In animal studies, such cyclical loading prompts cartilage cells to divide and replenish the tissue, he said.
It's so easy to forget how amazing our human body is and how perfectly designed it is. Happy running!