Think about this. Take a bodybuilder. He trains with high volumes to get all those sick pumps, brah. These sweet pumps improve vascularity, capillarry density (for more pumps), and the oxidative capacity of muscle. These are all Type I characteristics. People just automatically assume that weights=Type II fibers. This is just not true. When the majority of the earth were small hunter gatherer communities, there were no weights but humans still had the capabilities to sprint after and kill their food. Dyanamic and Maximal efforts. These are characteristics of Type II fibers. Humans that lacked these traits fucking died in terrible ways. Like, eaten by something they couldnt outrun or they starved to death. This is where the evolution of fiber typing comes in.
The body reacts to the stress placed on it. Tons of volume and muscular work results in adaptations in fiber size, intermuscular coordination (although limited), and neurological adaptations that all attribute to the gains you get in the weightroom. Your body recognizes the need to handle more volume, thus, Type I fibers grow and Type II fibers take on Type I characteristics.
Now, take some asshole who has never lifted a weight in his life. Due to the human races hunter/gatherer roots, that guy is going to have a higher distribution of Type II fiber area than a bodybuilder. Just in case a fucking t-rex breaks into his living room and he has to get out in a hurry.
He has had no stress to adapt to.
There are tons of studies on this stuff. They just don't ever get published anywhere that anyone except nerds like me ever reads.
When you really start critical thinking about all this shit, it paints a perfect picture of why no one can explain exactly what causes delayed onset muscle soreness... because if you got sore while you were running from a lion, you would die.