system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What happens in your body when you get a knot in your back?
gpt
A muscle knot is when the muscles in a particular spot are constantly contracted even when you are trying to be at rest.

If a muscle fiber gets hurt the others muscles around it will bunch up and contract around it to make sort of a protective shield, this bunching around the injured area forms a "knot". It's an involuntary response that you can't control mentally.