system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does getting a massage feel good?

Some people say a "knot" is a local spot where the muscle fiber has been injured, but applying pressure to injuries usually only causes pain. Is a "knot" a real biophysical thing, such as a spot where some chemical has built up? Can they be seen on an MRI, and does rubbing one make it dissipate? It seems to me that our bodies would only evolve that deep, satisfying sensation in response to having our muscles rubbed if it was doing something that helped our survival.
gpt
Muscle knots aka "trigger points" come from a build up of protein and lactic acid which causes restriction of blood flow and subsequently leads to pain and inflammation because the area is being deprived of fresh oxygen.

 When you massage the area it causes the muscle to relax which allows increased blood flow, bringing fresh oxygen to the inflamed area.