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UD research suggests physical activity strengthens joint health

Physical activity has often been assumed to wear down cartilage overtime, but University of Delaware researchers say that may not be.

Cartilage is a pore connective tissue filled with water that can last up to 40 to 50 years before experiencing serious wear and tear. UD biomedical engineering professor Chris Price said it is an important tissue because it lines the body’s joints.

“If we didn’t have cartilage, we would have bone on bone articulation and that would be very rough and that would wear away very quickly,” Price said. “The cartilage acts as a very slippery material.”

Fellow UD researcher and mechanical engineering professor David Burris said over time, water leaks out of cartilage, but he and Price want to know why some does not. They hope studying joint biomechanics and the biology of the cells within a joint in tandem will help.

Previous studies suggest the more physically active someone is, the more likely they are to tear their cartilage. But Burris and Price say activity is actually the engine of cartilage health because it pushes fluid back in. So they want to know more about the mechanisms behind cartilage recovery - internal pressurization and external pressurization. Burris compared the latter to hydroplaning in a vehicle.

“It's just a competition between rate of loss from weight of the car and the rate of recovery from you operating the car at sufficient speed to feed fluid back into the sponge,” Burris said.

When more fluid goes into the cartilage, some of the water is pushed out, he said. There are two main lubrication theories: One is that fluid within the cartilage provides lubrication. The other is that motion will build up pressure between the surfaces and create a fluid film. Burris and Price say both theories, combined, are how joints lubricate themselves.

What this means is when a person moves, they are exerting pressure on the fluid within the cartilage, and the fluid helps to sustain the cartilage and the joint.

“If you load your joint, we know that the water leaks out - we were interested in understanding why it doesn’t leak out,” Burris said. “It seems like it’s hard to imagine how if you load a sponge the water wouldn’t eventually all just leak out.”

Price said if they can better understand how natural joints work, they can better indicate how humans can use activity to better secure joint health. Researchers could also potentially re-engineer materials to create artificial joints.

Doing so, Price said, could mean creating artificial joints that last longer.