Connective tissue does not turn over at a very high rate, so when it becomes cross-linked it tends to stay that way. Cross linked collagen is what is holding the shoulder or other joint stuck in position.
What causes the cross-linking is a sugar and free radical reaction that oxydizes the collagen, making it hard and brittle. The same process turns an apple brown when it is cut open. The sugar and protein become fused when they are oxydized, it is called the Amadori reaction and is a major cause of stiffness for many. This is a sign that your blood glucose is out of control. And that your antioxidant defenses are down.
What to do?
1. Take a high quality antioxidant, like the one I use.