Researchers at the University of Leeds have determined that knights wearing full plate armor would have become exhausted while lugging 30-50kg of metal around the medieval battlefield, especially a muddy one like Agincourt. Being a bit tired is, of course, better than being rendered dead due to hacking with metal objects. Except that enormous numbers of French knights at Agincourt did wind up dead, apparently due to being too tired to prevent being lethally hacked with metal objects.
Ironically, the longbow may have won Agincourt, not because of the high velocity pointy bits it flung at people, but because of the exhausting measures people took to counteract those high velocity pointy bits.
Follow this link to see some poor bastard getting talked into running on a treadmill in replica armor. Then you can go to your nearest Renaissance Fair and understand why the reenactors spend most of their time sitting in the shade and very little time “having at thee”.