See, I'm 34C, and an underwire does not cut it when I run. Even when I was an A, I really needed a sports bra or I'd be hurting. I could get away with it for maybe fifteen minutes, but when I was playing soccer six days a week? I practically lived in one. So maybe Tsunade wouldn't wear one, but I don't think any of the other women in Naruto are too much bigger than me.