I feel the problem isn't as much the requirement as is the difference in comfort man and woman enjoy for a same job.
For example, this Scottish-inspired pub in a city I lived in. Both men and women were in Scottish-inspired wear. For men a kilt that covered their knees and reached to their calves. When they served food and drink, they could comfortably lean over and do their job. However, the women wore very short skirts that reached mid-thigh. Now, when they wanted to lean over to serve or to recuperate plates and glass, they were feeling much less comfortable, unable to perform optimally, etc.
Let's look at male flight attendants versus female. The male flight attendant is dressed in pants, flat shoes and does not wear make-up (hopefully, all of this is comfortable - uniforms can be very restrictive, whatever the gender). The female flight attendant is dressed in some flight companies (not all!) in a pencil skirt, wears small heels and make-up. Her movements are already restricted. She is expected to lift luggage, install people, serve them when her legs are kept constricted by a narrow skirt. As well, she works hard and sweats under her make-up, for me that would be a very distracting and disagreeable sensation. Again, the woman is not able to perform optimally. If she were allowed to wear pants and flat shoes, there are big chances she would be able to do her job in a more comfortable and efficient way.
This conversation is about specific job requirements aimed at women. However, we can broaden the idea of discrimination to men, too.
Why are men not considered efficient nurses, elementary school and kindergarten teachers? There is this presupposition, again based on obsolete ideas, that men are not as caring, as detail-oriented and as patient as women are. Again, when we go back into history, because men have a higher muscle mass, you would want them to focus on physical jobs as opposed to jobs related to care. Surgery in itself was a very, very physical job back in the days. Having been in and out of hospitals and having had a male elementary school teacher, I can assure that these preconceived ideas do not hold true. Every person should do what they are good at and thus, optimize life in society (we all depend of each other).
You can view it as an evolution of society's demand and the industry not keeping in train with them. Efficiency is being lost by imposing constrictive aesthetic or discriminatory standards on both women and men. We should aim for comfort as a means to improve overall global efficiency.