i don't think the real medieval knight would have been as fit,......too busy drinking and wenching
Actually medieval knights don't have to be cardiovascular supreme like today's modern soldier they just have to be strong enough to move and fight in full armor well enough in combat. They do drink and eat a lot because they have the best food given to them by their lords and king whom they serve. Their diet are better than the average serfs eats.
Additionally Wars of the period were more rare. Knights tended to be more like athletes training for either war or tournament. Tournament were regular affairs and a Knight who did well in the tournament could make himself quite the purse. As such a Knight would be spending a deal of his time training, and in daily activities like hunting.
Drinking was common but unlike today drink came in a variety of strengths and often included weaker varieties. Drink was also important for health as water was... well the word cesspool comes to mind. Beer is boiled which makes it safer. Wenching I'll let you have plenty of that going around.
now as to moving in full armor. Knights were trained from a young age to fight in armor and from period. Also keep in mind that knights did not buy off the rack they had their armor tailor made for them. infact medieval manuscripts show knights doing somersaults and back flips in well made armor.
The key differences though are how soldiers are expected to fight. Knights in combat were specialists. Infantry are generalists. Knights would be brought to a fight tat was expected. They maneuvered from a set start of battle. Infantry in modern times are expected to fight on the fly.
for a Knight it was, The Enemy is here we set up and attack.
For modern infantry it's we are here now where are they?
what is important fro the video though is that the weight distribution of a knight is better than the modern infantry fighting load. IE even if they are down to 50 pounds each that 50 pounds for a Knight is all over there body well for a modern soldier it's on the back and chest.
They are as good as the US Marines Silent Drill Team.