publico.es/ciencias/388738/l ... na-ventaja
In that link realte that a French army lost because they charged against the English army hundreds of metters, and after of that they haven't any strength to fight.
I think taht is a good flavour then the armour in te Core Rules, and the hard activities.
Hmm... There's an english version of this story floating around somewhere... 
And if it´s the one i think it is, it was basically based on "oh dear, we who havent spent weeks and months training to move in armour gets dreadfully tired awfully quickly, how shocking, obviously they cant be used without horrible fatigue..."(this also disregarding that there´s plenty of enthusiasts and alike who can do some pretty amazing stuff despite having a 10-15kg plate or mesh armour on them, like a ~20 minute acrobatics show i´ve seen for example).
Yes, ST should penalize walking hundreds of meters in mud up to the knees with some fatigue. I think it is fatiguing even without any armor.
laughs
I like the pun in the title post!
You forgot the uphill part. I'm pretty sure those dismounted knights were trying to charge uphill, in mud, and in full armor, while keeping their shields up against arrows.
At least they didn't ride down their own crossbowmen that time in a hurry to get to the enemy. 
And before you mock the French, they still won that war, eventually, so there !
I would never mock the French. Don´t want them catapulting various farm animals on my head after all... :mrgreen:
What they were talking about was how much harder the body has to work. Apparently humans are not well designed to carry weight on their legs, we like to carry it on our backs instead, far more efficiently too.
Sure its easier yeah... What i remember from the time i got a chance to try an armour on though, the weight is very well distributed and most of the weight is felt where it "should be".
I sometimes use weights on ends of arms and legs while training martial arts(up to 1kg/2kg respectively) and even though i´m totally not athletic or welltrained for that(it´s basically just a way to speed up yourself once you drop the weights) i can still keep that up for quite a long while, doing lots of moves that gets really straining with the weights on.
And as i said earlier, i´ve seen a guy keep up an acrobatic show for 20+ minutes in a full armour, and he had something like ~5 years of practise with the armour, "just normal" acrobatics and parkour before that.
And it´s not like he was really tired afterwards.
So yeah, as someone noted, getting stuck in mud and things, that can be tireing even without armour, but the idea that the armour directly caused too much fatigue to go fight, no i just have serious problems believing that.
(Be careful, m'lords, or he shall taunt us a second time!) 