Imagine the inner tube of your bicycle wheel is deflated. Imagine holding it in your hands; notice how limp and flexible it feels. You can bend it and twist it any direction you like. Now imagine the same inner tube filled with water. Try to flex it now and feel the rigidity that has suddenly appeared. Water, which normally seems to be quite yielding, is very difficult to compress. When contained, water provides a tremendous resistance to being squeezed. This is the basis of hydraulic systems – fluids, such as water, when they have been contained or constrained, resist compression and transfer forces placed upon them into areas of lesser resistance.
As was mentioned when we looked at our connective tissues, our tissues are filled with a variety of extracellular substances such as collagen fibers, elastin, etc. What weren’t described were the fluids that flow around everything. These fluids are called our “ground substances.” Sometimes these are called “cement substances” and they are found widely distributed throughout our connective tissues and supporting tissues. Ground substances act very much like the water in the inner tube analogy; they provide strength and support to the tissues. But they do so much more than just that.
Ground substances are the non-fibrous portion of our extracellular matrix (the stuff outside the cells of our bodies) in which the other components are held in place. They are made up of various proteins, water, and glycosaminoglycans.  Water can make up sixty to seventy percent of the ground substances, and it is attracted there because of the GAGs. One of the most important GAGs is hyaluronic acid (HA ). Various researchers have estimated that HA can attract and bind one thousand to eight thousand times its volume of water. Another estimate suggests each HA protein in the extracellular matrix has fifteen thousand molecules of water associated with it! Another important kind of GAG is chondroitin-sulfate.
When GAGs combine with proteins they are called “proteoglycans” and it is in this form that they attach to water molecules and hydrate our tissues. The proteoglycans are very malleable and move about freely. However, being made of water they also resist compression tremendously.
With water as a principal component of our ground substances, we can see why the ground substances are an excellent lubricant between fibrils, allowing them to move freely past each other. Water gives our tissues a spring-like ability, allowing them to return to their original shapes once pressure has ceased. This is crucial to our tissues’ ability to withstand stresses; however, a cyclic loading and unloading of the tissue is important to maintaining health. One study found that the alteration of loading and unloading of pressure on the tissue, as long as it is not excessive, maintains cartilage health.
The fluid in our joints (called “synovial fluid”) is also a lubricant and it too is made up substantially of GAGs. HA and two kinds of chondroitin-sulfates are essential to keeping our joints working properly.
When the extracellular matrix is well hydrated, cells, nutrients, and other components of the matrix can move about freely. Toxins and waste products can migrate out of the matrix into the blood or lymphatic system to be removed from the body. The ground substances, which are also formed by the fibroblasts (remember, fibroblasts also produce collagen), are also helpful in resisting the spread of infection and are a part of our immune system barrier.
Unfortunately, as we age, the ability of the body to create HA and other GAGs diminishes. We have fewer fibroblasts available to us, and those we do have produce less HA. As a consequence, the extracellular matrix becomes filled more and more with fibers. As these fibers come closer together, they generate cross-links that bind them to each other. As a result of that, our tissues become stiffer, less elastic, and less open to the flow of the other components in our matrix. Toxins and waste products become trapped in the matrix and cannot get out, but harmful bacteria can migrate around more easily. 
Fortunately exercise like yoga and massage, which stress the extracellular matrix, can help us maintain the number of fibroblasts and keep them functioning properly. This helps to keep the matrix hydrated, open, and strong.
We need these fluids everywhere in the body. The fluid of the eye is made up mostly of ground substances. Our skin needs HA to remain soft. Recently cosmetic surgeons have been using HA injections, instead of collagen, as a soft tissue filler to increase the size of lips or remove skin wrinkles. The effects, however, last only six to twelve months. Chondroitin is an often-used supplement to help increase lubrication of joints. However, injections and supplements are very inefficient ways to hydrate the body. More effective is to coax the body to increase its own production.
Ground substances can be fluidic or gel-like, and under certain conditions they change from one to the other. When they are gel-like they provide more stability, but they are less open for the passage of materials of the matrix. When they are fluid they have less rigidity, but more openness to the flow of materials. Compression of the tissues, via yoga and other means, can temporarily transform the ground substance from gel to fluid. During the fluid state, toxins and wastes can be transported out of the matrix. Once again, yoga is an excellent way to detoxify the body.
- — That’s a mouthful, which is easy to gag upon when trying to pronounce. So let’s just call these GAGs for short.
- — To be more current, we could call this hyaluronan.
- — Called “ama” in yoga.
- — One study showed that oral ingestion of chondroitin-sulfate resulted in only a five percent absorption rate, which meant that large doses were required to have any effect.