I often hear from my patients, friends, and acquaintances that they would exercise more if their joints didn't hurt so badly. Sometimes the person will say something to the effect of "I don't see how exercising can be good for me when it hurts like this!" The short answer is that there, unfortunately, is not a short answer. However, that's why I made this blog post...because the answer is detailed and needs to be fully explained so that those with arthritis and those who work in fields of physical activity understand why. This will be a multi-part blog post so that you don't experience death-by-blogpost.
The first thing to understand is how joints are maintained. They differ from most tissues which receive blood directly and are supported by the oxygen and nutrients in blood. Instead, cartilage is supported largely by the fluid within the joint itself. We call this fluid synovial fluid because the membrane covering a joint is called the synovium. The synovium produces the joint fluid directly from blood by taking all of the cells and large proteins out of the blood and leaving a glucose rich, oxygen containing fluid which much resembles blood plasma.
That's all well and good, you might say, but how does this help me? Well, cartilage, like other tissues in our body, requires nutrients and oxygen to repair itself. Exercising the muscles around that joint actually increase how much fluid that joint produces. To a degree, more fluid should lead to better repair of that joint's cartilage.
The two large forces behind synovial fluid production are linked to one another: larger range of motion and more muscle recruitment. In general, larger ranges of motion tend to recruit more muscles and muscle fibers. These additional fibers require additional blood flow, and the arteries which carry this blood also supply the joints around which the muscles act. Take for example walking a flat treadmill versus riding an exercise bicycle. In both exercises, you move at the hips, knees, and ankles; however, with the bicycle, you are recruiting more muscle fibers by the larger movements of your legs and feet. As a general statement, exercise bicycles tend to be great for increasing blood flow and thus joint fluid production.
In the next post, we'll talk about joint stiffness and the forces which act on cartilage and what forces to avoid and which ones are beneficial! As always, I'll take the jargon out of it. Tell me what you think by commenting on the post. Which exercises do you feel really "warm up" your knee or hip??