system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what happens to a muscle when you pull it.

Pulled a muscle in my back yesterday and was curious what is actually happening when you feel that initial pain and the soreness after.
gpt
When you  strain a muscle you are actually stretching it beyond its normal limits.  There are different grades of strains. You can pull the muscle and not  damage it in some cases and in others the muscle fibers actually tear. A  grade 3 sprain is when you pull the muscle so hard that it tears  completely and may require surgery.

Picture walking and turning you ankle. It may be mild or a grade 3.

A sprain is basically the same thing but involves the tendons and ligaments. Again there are three grades.

Each can be as painful of the other and you can get a strain and sprain at the same time.

The pain remains as the muscles, tendons or ligaments need time to heal.