Men need to be in better shape as they will most likely die on the battlefield if they are not, women are seldom put in that position because military leaders know that when a man watches a women die from a hostile target they forget their training and act irrationally. If they don't push infantry men to be their best and hold them to only what a women is physically capable of they will not be in their peak performance physically to take lives the lives of enemy combatants.
Men are stronger in other ways than women are. Therefore if they had to do the same things that men did they may fall back and have a bad performance when it is time to go to war.
