So for all y'all 'Muricans worried about the draft, here is how people got out of the military once in basic training in the military I was in (Danish Air Force):

1. go to the doctor and say your back hurts.
2. doctor says there's nothing wrong with you and maybe gives you some painkillers.
3. go back again and say they didn't work and your back still hurts.
4. doctor says they still can't find anything wrong.
5. repeat step 3 a few more times.
6. eventually the doctor will say they can't find anything wrong but they also can't tell you that your back doesn't hurt.
7. dismissal on medical grounds.

I know a few people who did this and it worked. Took them a couple weeks in total, going back to the doctor every 2/3 days.

Edit: to clarify; the reason this works is cos the military compensates you for injuries, and the spine is always a tricky one so they don’t wanna risk you fucking it up and they have to pay a small fortune to try fix it for you.