You loose Fight, when the Opponent succesfully delivers a Blow to a vital area. You can be the toughest guy in the World - when someone's Fist hits your Throat (for example), you are done for...
There is a significant Difference between 2 Guys, beating themselves up in a Bar - and a close-quarter Fight in a War:
The Guys in the Bar really don't want to kill each other, so they simply trade blows to non-vital-areas for a while, and 5 Minutes later they enjoy a Beer together...
In such Fights the toughest Guy always wins. Stamina and Strength are the key components in winning here.
In our civilized, modern World we are (luckily) so accustomed to this kind of Fight, that we have Problems imagining other kinds of fights, like a lethal Fight in a War. Even MMA Fights have Rules and are relatively harmless (at least a friend of mine who does MMA keeps saying this...)

Winning a lethal Fight means protecting your vital Areas and delivering ONE successful Hit. Plain and simple. You need neither extreme Strength nor Disco-Dancing-Moves to do that. The quicker and straighter your Moves, the higher the Chances of hitting your Opponent.
Sure, you have to have some kind of Strength for your Blow, but let's assume that EVERY Soldier has recieved a bit of training, regardless of Gender.

I know, we all like the Imagination of an Amazon moving smooth and slinky on the Battlefield like a perfect blend of an attacking Tiger and Ginger Rodgers having a Dance with Freddy - but let's be realistic, here: You'll skip the Hey-Look-at-me-I'm sexy-Attitude, when your life is at stake...