I was one who virtually never dressed out for or participated in gym during Jr. High. Why? It was a stupid waste of time…running around in circles and doing idiotic drills…and I had zero interest in it. Had we been maybe going outside and playing soccer or even allowed to just play a game of basketball instead of doing insipid DRILLS, I would SOOO have been up for it.
FTR, I felt the same about ALL my classes and pretty much “sat them out” as well (failing the 7th grade altogether).
I went on to spend a yr in a religious school (as parental punishment) where I “worked at my own pace” (meaning I did nothing) and to drop out at age 16.
At 18, I went and took the test and got my GED.
A few yrs later, I went to college and graduated with a 4.0 gpa.
I’m currently back in school working on my second degree and carrying a 3.85 last I checked.
In between, had 2 successful careers, owned 2 small businesses, had 2 kids, and generally did OK in life.
So why did I protest gym by refusing to dress out? Because it was stupid, boring, an insult to my intelligence AND the uniform was this polyester, navy blue striped monstrosity I couldn’t STAND! 
The rest of school was everything BUT the bad uniform (oh, except the religious school, which also had one of those).