Today is my last day in construction. My body is really dragging after 5 weeks of this. I don't know how other men do it for so many years.
Takes almost a month just to get your feet/legs used to standing all day in steel toe boots. And then of course the lifting and general aches and pains (depending on what you are doing).
But you do eventually grow amazingly strong and develop the specific stamina needed for whatever type of labor you are doing.
I did a couple years as an industrial scaffolder, after mostly being a guy that sat around and read a lot. After getting over the hump it didn't feel so bad. When we did nonstop shutdown work (7 days a week, 12+ hours a day), okay, that wore you down pretty fast. But five tens of pure physical workload each and every day soon became pretty easy.