How do I keep doing physical trade work when my body is wearing out?

You can find any fault by feel and reason, and your body is paying the bill for years of the work. That is the hard bargain of a skilled trade. The knowledge in your hands took decades to build, and the same decades wore down the frame that carries it. Both things are true. Don't wait for your body to force the conversation. It is already telling you something, and honoring it now is not weakness; it is the same good judgment you use on the job. The goal is to make your experience carry more of the load and your back carry less. Your value has shifted from what you can lift to what you know, and that knowledge is worth more, not less. Pick one way to trade strain for skill this year. Train an apprentice who does the crawling while you do the thinking. Take the diagnostic and supervisory jobs. Consult, teach, inspect. Start one conversation about a role that uses your head more and your body less. You spent years earning that knowledge. Let it start carrying you.