Reading this felt like you've been observing me at the gym and documenting my behaviour. I've been trying to establish an exercise habit and at some point I'd like to become comfortable again talking to strangers. It used to be a skill that I practiced unknowingly when I was young and could talk to anyone. Now there are days when I'm done working out and it takes all the effort just to make eye contact with someone and mutter something like "hey, how was your class?"
Don't get me wrong - many introverts can talk to strangers just fine if they need it (just as I can lift 50 lbs if I need it), it's just something they don't particularly enjoy doing. It's work. If it needs to be done, it will be done, but if it can be avoided - it will be avoided. I am not sure one needs some training to change that - if I don't enjoy doing something, why waste time on doing it if I could instead do something I already enjoy doing?
for an ice-breaker, dont go with an emotional check-in lol. much easier to say something humorous like 'fukin weights, bastards are gonna kill me rather than make me fit'