system
Given the following post, respond as if you're commenting on Reddit:
human
What happens to your muscles after you warm up? Why does it result in a reduced chance of injury?
gpt
The primary thing that affects your muscles with a warm up is blood flow.  

At rest, most of your skeletal muscles receive very little blood flow, because they aren't doing anything, they just kind of sit there.  When you do a *proper* warm up, those muscles start to need more substrates (oxygen, triglycerides, glycogen/glucose, proteins, all kinds of stuff).  In order to deliver those substrates, your body pumps more blood to those muscles.  That's the major thing that happens to your muscles during/after a *proper* warm up.  

As for the injury, think of your muscles as being like a sponge.  Before a *proper* warm up, your muscles are like a dried out sponge.  They are stiff, rigid, and prone to do things like crack and break, just like a really dry sponge.  When you warm up your muscles "soak up" that blood, and like a sponge that soaks up a bunch of water, they get soft and flexible, and instead of cracking or breaking under strain, they bend and flex.