Ligaments are composed largely of elastin, a stretchable fibrous protein. Tendons are made of collagen and are essentially inflexible. When pushed beyond their capacity, tendons can develop microtears. Glucosamine and vitamin C play a role in the formation of new collagen. Most athletes eventually experience joint injury.
Various traumas can harm the cartilage that lines joint surfaces.
Cartilage, a plastic-like tissue, is made of thick bundles of collagen. It functions as a shock absorber, cushioning the joint with every movement. Both substances continuously construct and reconstruct cartilage. Glucosamine is the major precursor of GAGs. The synthesis of glucosamine from glucose and glutamine is the rate-limiting step in GAG production, and hence in repairing cartilage.