I asked about carrying weight in a rucksack not about splitting wood, what is mainly a technique and less a question of body force.
The question here is, if the 1/5 recommendation comes from Baden Powell as a jungle war experience and was proofed in the boy scouts, where it fits, and than simply copied to the girl scouts.
I think, that's possible.
I always went for hiking with women who had been smaller and less sporty than me.
But my brother has a really strong wife (they are farmers) and got the impression, that he can't give her the same load in the trekking rucksack like a man in the same size and age. It works in the beginning but he gets problems in the end of the day. He usually hikes in the Austrian Mountains, where he can't construct the tent everywhere, when they get tired.
He came several times in really dangerous situations in the mountains, and so we started once more to think about the problem.
Is that -20% a very rough thumb rule, because women are 20% smaller than men?
Or does it mean, that a woman off the same age, size, weight and training should carry 20% less than a man?
That would mean round about 20% less because she is smaller than the man, and once more 20% less because she is female?
My own experience is, that indeed the women who were trekking with me could walk comfortably in the same speed next to me and the same distance, if they carried round about 60% of my rucksack weight, but got real problems when they got on shorter distances in the evening additional food and water in the rucksack.
I know, that I am compared with other men relatively strong, and off course it's possible, that the women who came with me had been exceptional weak. But I was hiking with several young women, and it always was the same: Compared with boy scouts in the same age and size, they couldn't carry the same load, and I mean young, sporty and motivated people between 15 and 20 years age.
So the question is: Round about -20% or round about -40%???
Yes, of course, there are individual exceptions. Little girls can become stronger than taller men, it's just a question of training.
Once we were sitting in a train, a young girl entered with a violin suitcase and I joked, if there was a Kalashnikow in. She opened the suitcase and took out a sport bow, which nobody of us was able to suspend. Even me, who was a head taller than her.
But this young lady shot with that bow four weeks earlier at the Olympic games!
After she told it us, we had been very glad...