It's common knowledge that push-ups can be made a bit more manageable by assuming the position pictured above and resting your weight on your knees instead of up on your toes. The term "modified push-ups" is used by many workout websites, shows, and videos to describe this exercise, but who hasn't more frequently heard them called, simply, "girl push-ups"?
"Girl push-ups" is what they were called in every single gym class I was in as a kid, anyway. By both the teachers and the students. The teachers let us know that girls were welcome to do our push-ups on our knees, while boys had to do "real" push-ups. I remember looking around and feeling intensely sorry for boys who obviously couldn't keep up with the more athletic guys but weren't given the option to do the exercise that was more manageable and comfortable for them. Meanwhile, there were always a few athletic girls who could have easily done their push-ups while up on their toes.
Designating exercise guidelines by gender rather than by ability promoted the message that ALL girls are weaker than ALL boys. ALL the time. Any exceptions to that rule were just that -- exceptional. Girls who could do "real push-ups" were considered super strong, and therefore not girly, while boys who could not were considered super weak, and therefore not manly. (Ever notice how the opposite of "girly" in this scenario is "manly"? "Boyish" doesn't quite work when one is trying terribly hard to prove one's masculine strength.)
I don't know how push-ups are handled in phys ed classes today, but I can't imagine that push-ups on one's knees have lost their reputation as "girl push-ups". I can only hope that requirements of what exercises are required are no longer explicitly based in gender. Maybe I'm just being optimistic, though.