system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do your muscles feel "good" when you stretch them?

After sitting for a while you get stiff from not moving. When you take a break and stretch a little, why does it feel so good?
gpt
When you stretch, you create micro tears in your muscles. Your brain releases endorphins, the feel good stuff, to cover it. As long as the tears are small, you feel good. When the tears are big, like when you tear a pectoral muscle, sorry bud, them endorphins just won't cut it and you scream bloody murder.