This semester, I completed observations on sexism for one of my classes. I was astonished at how much sexism is still evident, even with changing laws and some attitudes.
The most ridiculous incident was when I was told at work that I wasn't allowed to go up a ladder to get supplies because I'm a girl. I needed to find a male to get the supplies for me. This was the owner's policy (a male, surprise). Policies like this perpetuate the stereotype that women are helpless and are too delicate to do the same things men do. These policies also don't allow for any individual variation; they generalize to all women.
While it may be the trend that most men are physically stronger and bigger than most women, this is not true in all cases. Some women are more capable of physical tasks than some men. These stereotypes hold women back from being able to pursue the same opportunities as men.
Be aware of the things you are saying and/or doing, and think about what the underlying messages of your statements are.