Synovial Fluid

I'm reading Eckhart Meyner's "Horse + Rider = 1" which is pretty great 80 pages in. I'll have to write a review when I'm done.

In a section about warming up properly, she writes, "By warming up, you can improve the nourishment inside the joint cartilafe, and after a while, the cartilage layer in the joints thickens. After moving a joint for five minutes, the cartilage-nourishing synovial fluid increases--a process that is concluded after about 20 minutes. ... The horse should move at the walk for at least 15 minutes before any actual suppling work starts."

Well now. I am a firm believer in warming up because of the mental benefits, but I probably don't ever walk for 15 minutes. Actually, I know I don't. But if there were serious and long-term benefits to doing so for the thickness of my horse's cartilage? Sure. I'd make the change in my habits, both for me and my students. Let's dig into the internet realm of research.

First of all! What the heck is synovial fluid?

Synovial fluid is a non-newtonian fluid* (which makes the physics nerd in me so so so happy - have you ever seen me play with Oobleck?). The two primary functions of synovial fluid are to carry nutrients to cartilage and to reduce friction between pieces of cartilage in synovial joints (basically all the moveable joints are synovial).


Synovial fluid is so nourishing to cartilage that there's a thing called "joint mice", where a piece of cartilage breaks off and falls into the joint cavity and then grows and stays alive because it's being bathed in synovial fluid. This lends some credence to the cartilage layer thickening if synovial fluid is increased, allowing the cartilagenous parts of the joint to be further bathed in the hyraluronic acid and plasma that make up the synovial fluid.

A quick search of "synovial fluid warm up" produces a bunch of yoga blogs and the like informing me that a good warm up allows increased production of synovial fluid to lubricate the joints. Fantastic! Where are your resources whyy. A good point of one of these blogs was that moving the joint allows the synovial fluid to circulate - this follows common sense, right?

I then did some research into synovial fluid production.

One method of joint lubrication is referred to as "weeping" or hydrostatic lubrication. I understand it somewhat simply like this: if a sponge is wet, it might not be dripping, but if pressure is applied, the water will come out. Cartilage in a joint is sort of like the sponge - synovial fluid is contained within the cartilage and when pressure is applied, the fluid weeps out to fill irregularities in the cartilage and provide lubrication. Through movement, the fluid seems to be maintained, and failure of joints due to age is likely a reduced thickness in the cartilage or increased 'bumpiness' and irregularity of the cartilage.

The other method of joint lubrication is called "boundary lubrication" where the load is borne primarily surface-to-surface.

As far as I can understand from my reading, hydrostatic lubrication occurs at the onset of motion, and boundary lubrication mostly takes over as the hydrostatic pressure lessens.

Alright. I yield. I can't find any hard evidence, especially surrounding the whole "synovial fluid increases starting at five minutes and stopping at twenty" sort of thing, but who knows. Maybe I didn't dig through the right places. I did learn some interesting new things about joints.

Random facts I learned in this research:

1. Prosthetic joints heat up faster than real joints if you're walking for a long time, and synovial fluid is at risk for breaking down and losing its lubrication powers if the joint gets too hot.
2. If you want to get better at doing things in the cold, your improvement will be really big from the first day of trying to do things with cold hands to the second day, but there will be no further improvement. Sucks to be cold.
3. Heat-killed bacteria can cause arthritis.  
4. Salt-water doesn't work very well as a joint lubricator. 
5. It's difficult to wash hyaluranate and synovial fluid off bones. 
6. I learned a new word! Viscoelastic

*Non-newtonian means that the fluid changes viscosity (thickness) when pressure is applied. Oobleck becomes thin when you press on it, and nearly solid when you're not pushing on it.