>>76288306 (OP)From what we know (armor, illustrations, etc), extremely skinny, prettyboys (with beards as they aged ofc) and tough as nails, beating other people and each other to death just for fun (so the Church had to step in unironically). Imagine you look like a skinny fashion model, but you're a pro athlete, but your sport is killing other pro athletes in armed combat (and sometimes unarmed too). So yeah, the cringe manga bishounen "nothing personnel" ideal, pretty much. They mostly did ballistic exercise like track and field-ish and basically ate no vegetables, only daily pounds of meat and bread with some fruit and lots of wine. We don't know exactly HOW they trained, only what exercises they generally did, which was throwing, jumping, sprinting, fencing, wrestling, hunting animals armed and unarmed etc. We also know they kept the light physique until old age and also were still able to fight in battle in their 70s and sometimes 80s like some warlords of antiquity did.
So, tl;dr, I guess those skinny MMA guys would be kinda sorty the build you are going for, but remember, the building of mass, muscle or fat, wasn't wanted. You also need long wavy hair, pale skin and smooth features I guess.