As a long time lifter myself, I get where you're going.

Anytime i can get away with sitting while doing a task, i do it. It saves the feet, and if everything is at the right height, your back and shoulders too. Good examples of when, is marking out lay lines, hand sanding, and filing. Unless it's something like a dremel hand piece though, i'm standing when it comes to power tools. If you want to take the sitting a step farther, look at how the tradition japanese smithies are set up. i've seen instances both in that culture and the middle east where they had set up everything where they could somewhat comfortably sit while forging, while the apprentices/helpers are standing and using the big sledges.

The other factor for me is time. This is still at the hobby level for me, and probably will remain that way since the all mighty day job brings home the bread. Unless im really focused, i'm only working on something for 1-2 hours at a time which seems to really help with only getting minor aches and pains. 

Full time blacksmith (no power hammer) and also life long lifter, the last 12 years following the Starting Strength method. Taking a stab based on what you wrote, I would try looking at how much sleep you're getting and how much food, especially protein. For myself, I try for 8 hours a night and as I've found it hard to get the protein I need from just eating, I add at least 50 grams a day with whey protein.

I don't lift anymore, but have a full military career, as well as 35yrs of Blacksmithing/Bladesmithing under my belt.  I also suffer from Lupus, which in my case has caused interstitial lung disease, kidney disease, and Fibro. Which means there a some days that I literally cannot get off the couch when things are flaring up. 

  I personally have/use power equipment..... only because a long time ago, I had several old, life long Blacksmiths tell me.... "If you want to keep forging when you're old and gray, get yourself a power hammer and a press NOW"... and I did. 😊   Now that I am "old and gray", without the air hammer and the forging press, it's very likely that my body (because of the Lupus and it's associated issues) would have put me out of the game. 

  That aside, the one thing I have learned in all the years of teaching Bladesmithing, is that NOTHING in terms of "lifting" or specific exercises can duplicate what the body does when we hammer hot steel.   I once taught a Basic Bladesmithing class to a then "Mr. Minnesota".  He was a huge, very heavily muscled man, and frankly I was concerned that he was gona break some hammer handles.  However, I quickly found that even with all that well defined muscle mass, he couldn't swing a 2 1/2lb hammer more than 10-12 blows without wearing out/resting. Why? Because swinging that hammer used his muscles in a way/manner that he'd not done before.  He had not developed the forearm strength for hammering, nor any type of "work rhythm."   Just an example of... you really have to "do it", to become "strong" at it.

  Nothing about Bladesmithing is "easy".  Forging takes strength in the right places, building a working rhythm, and doing it enough to create muscle memory.  Hot steel, by it's nature is dangerous.   The moment you fail to respect it, or loose your concentration....that's when it will get you.  Even more so if you're doing it with a power hammer and/or a press, as the potential is there for much greater injury.  

 Here's another one....Grinding. It simply requires your FULL CONCENTRATION.  I tell students all the time when we get to "grinding day" of a class..... "Expect to be totally mentally exhausted by the end of today", and typically they are. (I think some are more frustrated....but even that drains a person.)

  As Matt mentioned "breaks" which are of paramount importance not only when learning to grind, but especially as you gain experience.  

  Mark made mention of having tools at the correct height (FOR YOU)....which is another MUST.  Your shop MUST be set up FOR YOU.

 And Gerald spoke of getting enough rest... so that you are mentally sharp, and your physical strength/endurance are there.

  ALL very wise words.

  I'll leave it with this... Not only does Bladesmithing require both physical and metal strength..... But, there are also some days, when Mr Muphy seems to be riding around in your back pocket.  Days when nothing seems to go right from the moment you stepped through the shop door. It could be a physical ache or pain, or a mental distraction that you can't seem to shake. But whatever it is, you're mind/concentration simply isn't on Bladesmithing/Knifemaking.  On those days, I walk right back out the door, lock it, grab the truck keys, fishing poles, and the dogs.....and off we go.   Even a "bad" days in the Montana mountains, fishing beaver ponds for Brookies and Rainbows, is better then even a slightly frustrating day in the Shop. 😉  

Thank you all for the feedback.  I guess what I meant when I said I lifted, took care of myself, etc is that I take my health very seriously.  Not that I expected any of that to offset what we do in the shop.  I have my grinder, anvil and my tools setup at the right working heights and I'm still walking away with slight neck pain from grinding and soreness in my feet/arches at times.   I wrote this inquiry hoping that outside of taking breaks there were other things I could do to help lengthen the working time in the shop.  

building up slow and not pushing through.. I blew out my elbow years ago , pushing through an order of tent stakes of all things.. spent a lot of years in pain recovering from that. 

Good technique helps, ie keeping the work hot , safe effective hammer grip and swing etc. and removing anything that causes pain. I had one of the 3m powered respirators with the face shield, I had to replace it with a clean space unit, the 3m was so heavy I was getting neck pain from the weight looking down to grind.  grinding especially swords beats my body up way more than forging even with out power hammers and presses.   

MP

Speaking for myself, to enable myself to work without pain and injury is the primary reason I do resistance training. I'm careful in the gym to avoid over-training arms and shoulders while at the same time strengthening them, and at 63 it can be quite the dance. Other then the occasional elbow twinge from pushing to get a job done, I have no shop related aches and pains.

The reason I suggested looking at your sleep and eating, is you said you were doing three stress activities, lifting, wrestling, and bladesmithing. Each of those incur a high recovery need, without sleep and food, this can't happen. If you're already getting plenty of sleep and protein, then possibly the three activities are leaving you in a state of over-training. I spent most of my adult life in a state of over-training. I looked good and felt good, but never got the results I hoped for, and that lasted until my early forty's and my body said “enough is enough” and started to break down. At the point of stopping with the weights, I came across the Starting Strength book by Mark Rippetoe and it completely changed how I train.