Hello and sorry for the hiatus! I've been working on a bit of research myself, and I hope to publish it soon in one of the sports medicine journals I regularly read! But back to the topic of how exercise improves arthritis. Last post, we talked about the means by which the cartilage of a joint is nourished, primarily by the joint fluid - also known as synovial fluid. We also explored that joint fluid is produced when the joint itself is moved by your muscles, thus more movement in these joints means more nourishment and repair of joint cartilage.
Today, I'd like to talk about joint stability, its impact on arthritis, and the manner in which exercise affects joint stability. First, it's important that we recognize that stability within a joint helps maintain cartilage. Let's think of the idea this way: your cartilage acts as a cushioning tissue for your joint to absorb impact and to reduce the effective impact that your bones experience. If a joint, a knee or a shoulder for example, is less stable, then the cartilage inside that joint shifts and moves more easily. Too much movement, in the case of a loose or unstable joint, means more cartilage wear and even movement in ways that the joint isn't meant to move. The classic example is a knee which loses a valuable ligament, the ACL, due to a traumatic injury.
The ACL, or anterior cruciate ligament, stabilizes the knee joint in a front to back manner. The above image, taken from the website of the American Academy of Orthopedic Surgeons, demonstrates the ACL if you were to look at your own knee in the mirror. For orientation, the kneecap, or patella, is located at the front of the knee. The ACL runs from the back of the end of the thigh bone, or femur, to the front of the shin bone, or tibia, where it attaches. It acts to stop the shin bone from shifting forward.
In the case of an injury to the ACL where it can no longer perform it's job, the knee becomes too loose. Medical professionals call this "joint instability." Below is a video demonstrating an exam maneuver which highlights the increased movement within a knee which lacks a functioning ACL.* Skip to time 0:39 for demonstration of the exam; exam ends at time 1:30.
Loss of the ACL in knees greatly increases the risk for arthritis. The converse is also true, a stable joint is less likely to progress toward arthritis or worsen already-present arthritis. In some athletes, things like the ACL may already be torn, or they may already have an unstable joint. If that is true for you, then of what use is this information? While there can be little done, outside of possibly an operation, to reconstruct or tighten ligaments, athletes and patients can absolutely improve their joint stability through exercise! How is this?
There are two kinds of tissues that keep a joint stable: passive and active. Passive tissues (also known as passive restraints) are things like cartilage, ligaments, the joint capsule, bony anatomy, etc. They're called passive because they work regardless of what you do. If I pull on your knee, it will only move so far and in only a certain direction because of passive restraints within and around your knee. Active restraints are essentially muscles and their associated tendons. Going back to the example of the knee, if I pull on your knee while your quadriceps and hamstrings muscles are tensed, I'll be able to move your knee much less if at all!
So what's the take away point here? When you improve the strength, resting tone, and endurance of your active restraint tissues (i.e. your muscles and their associated tendons), you decrease unwanted and excess motion within a joint, sparing your cartilage unnecessary grinding and wear.
How do you incorporate this? Two things: make sure that your muscle has strength and endurance along the entirety of its range of motion; strengthen all muscles that act on a joint. Interestingly, studies on muscular physiology shows that you can strengthen a muscle within only a certain range of motion if you only exercise it along that range of motion. The example would be going into a deep squat versus a shallow squat. If I only squat six inches down, then I will only be strong in a squat if I stay within that six inch range of motion. If I practice squatting to the full depth of my range of motion, then I strengthen all the muscles used in a squat along their full ranges of motion. Regarding the second point, if I only strengthen my quadriceps (the muscles on the front of your thighs), then I will overpower their opposing muscle group, the hamstrings (on the backs of your thighs), and cause a muscle imbalance. Muscle imbalances extrinsically change the way in which a joint moves, setting the motion of that joint into an improper alignment and into a pattern which will generate inappropriate wear of your cartilage.
1. A loose joint will likely become an arthritic joint
2. Improving muscular endurance and strength helps to bring joints into proper aligment
3. Be sure to use a muscle to it's full range of motion
4. Be sure to use all of the muscles which act on a joint.
What do you think? Have you noticed an improvement in how stable your joints feel after you've exercised for a few weeks? Comment below and let me know!
Selected Reading https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4337591/
*Note: I have no relationship, financial or otherwise with Dr. Janssen whose video is shown above.