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

I always wonder the mechanism of how rubbing muscle can make one feel good. It might be somthing about chemical reaction related to blood circulation and oxigen supplyment. How and what part of our body contribute to feel it?
gpt
A few reasons. Firstly because massage relaxes the muscles, reduces discomfort/ pain (by pain gating mechanism through the spine), promotes blood flow and helps to  strengthen the muscles and joints. It's beneficial effects also include endorphin release in the brain, which is similar to morphine (= relaxation, well being, bliss) 

Secondly, massage has evolutionary  roots. Grooming is part of our ape + developmental  past and it clearly *still* helps with personal/ group  bonding and the additional  psychological benefits.