I disagree with my gf's view on differences between men and women in athletics
Is it because of any particular reason?
Yes, my gal seems to think that women are more athletic than men.
Not everyone can have the same opinion. With significant others, we have to learn to be able to disagree without it being a source of trouble. You can respectfully disagree with her.
I still don't understand.
Just because she thinks something is right doesn't make it so. You could also be wrong but you should not fight over it.