I did kickboxing for awhile, always wore a binder ofcourse. And I used the male changing room, there were only a couple females, I was completely accepted as male (but I was on T).
I have always found binders extremely uncomfortable. The worst bit being putting it on, but I think 80% of the discomfort is the hate!
I also go to the gym, and I find that I can develop chest pains. I can be short of breath even though my fitness level is very good (Im fine doing stuff without a binder, I dont get the pains or breathlessness. I can pass fine without a binder, wearing a shirt or hoody etc but prefer a tshirt for sports obviously :p). Ive unfortunately reduced the amount of times I go to the gym recently, because of the discomfort. I just start to overheat (and I HATE being too warm :p ) and it feels like my ribcage is being pushed together in the centre, where my breastbone is.
I have heard that you can develop problems through binding and physical activity, but then again, this is just stuff I have heard. Id say youre fine to do sports, and no you dont have to prove you are biologically male to join a guys sports team (just beware of any "initiations" say, at uni, I know the rugby team has guys streak!) and you shouldnt develop problems. I think the main problem I have that I let effect me, is that I get too hot, therefore, I get miserable!! Haha.
And Happy Christmas everyone!! (I know it wont be Christmas yet for everyone, but it is here in England

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