Cady,
I get the Japan Woodworker catalog and check up the web site frequently. I don't look at Hida Tools much, but I have a nice collection of Japanese saws, chisels and all sorts of odd planes, new and used. Everytime I go to Japan I used to pick up something, first at the flea markets. Then a friend warned me that some tools were deliberately made to look old so us gullible foreigners would buy them, so I started picking them up new in tool stores. Love 'em. I am also eyeing up some replica old Stanley and English planes and tools that duplicate hand tools from the 1800s and early 1900s. Very Steam-punkish. I love old tools. I even try to use them, when I have the time, to make crooked furniture.
Back on topic: One of my teachers once stuck a 14th Century kabuto on my head and boy, it was heavy. If I tilted my head ever so slightly, the weight would disbalance me and cause a terrible strain on my neck. So I imagine having good posture and balance would sure go a long way to being able to endure wearing and fighting in that armor. Likewise other movements: what works in full armor is probably going to be good balance, posture, body alignment and movement. Take off the armor and it should be even faster and more efficient. It also helps if you have muscles that can endure long stretches of horse-riding, walking, running (to and away from a battle), etc. General labor helps, but you still need particular exercises and training of the proper kind.
I mentioned this in another thread, but I have students who have been training for years, and they still have problems with their basic stances and movements. I correct, they do it reasonably well one or two times after, and then their body snaps back to the way they are "used to" doing it, without proper alignment, proper muscle usage or timing. The body has not been trained from youth to move in that way, so one hour a week they fight a lifetime of muscle and body patterning, and they constantly lose. If they had the muscle and body vocabulary to begin with, they would have gotten menkyo kaiden or its equivalent by now. I suspect that could be the reason why many "greats" in ages past may have taken but a few years to reach mastery level, and why it takes many of us years and years (and perhaps decades) to reach that level. The basic foundational skills are so hard to reprogram into bodies that have been misaligned from childhood to yank with arms instead of hips, push instead of pull, use shoulders instead of lower body, etc.
Attached: an old 1970-ish photo of Donn Draeger (in yoroi) and Otake sensei doing Katori Shinto-ryu kenjutsu kata in Hawaii. Note Draeger's very good posture.