the current understanding of how tendons respond to loading, unloading, ageing and injury

A muscle contract, transfers load across the tendon into the attachment to another bone on the other side of a joint, sometimes across 2 joints. There can be a mechanical flaw/injury in the muscle or tendon, or the joint, if inflamed, can neurologically inhibit that muscle-tendon team. The journal abstract has a nice diagram looking at the potential cellular and molecular changes at the tendon interval.
"Here we review the current understanding of how tendons respond to loading, unloading, ageing and injury from cellular, molecular and mechanical points of view. "- S. Peter Magnusson, Michael Kjaer

https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP275450