It has been historically acknowledged that a woman does not have the upper body strength to be in ground combat operations; but those lines became blurred in Iraq (the need for women to search other women because of muslim sensitivities): which isn't a bad thing because the doctrine of COIN requires winning the population.
I know what you are thinking: we didn't win the population. And that my friend is a different argument: Is current U.S. COIN doctrine valid for a Muslim population?
That is a military-academic question.
And to add to your information, NPR recently learned of this requirement and whined all over the place saying it was descrimination..... of course NPR doesn’t understand that upper body strength is needed not only to possibly get yourself out of a dangerous situation, but also to be able to rescue your brothers in danger. They don’t care as long as those mean old Marines don’t descriminate against weaker individuals.