I have the tired arms experience as well. I also feel very faint when my arms feel like that. It helps to lie down.

It's not awful just kinda weird. I think maybe exercise might help. I need to up my weight lifting a bit. I get lazy because I'm a boob sometimes! Lol. I just hate no breath but I need to suck it up and work harder.

my legs feel extremely heavy sometimes, don1t know why

I also get a very tired feeling in my arms from time to time. Don't know if it has anything to do with this disease or not. Haven't had it in awhile though. Hope it gets better for you.