[Suppafly]

>Maybe an electrician, plumber, carpenter can weigh in

Those trades mostly pay their dues when they are younger and then the next batch of journeymen and apprentices take over that part of the job as they move up into the less physically demanding parts of the job. Even fairly physical jobs like bricklaying, they'll have the older dude doing nothing but slapping the bricks in place, they get carried over to him by one guy, one guy is mixing up the mortar, one guy is unloading the truck, another is touching up the joints, etc. It's one of those things that explains why union jobs have so many extra people too. It's not one dude doing everything, it's 3 guys doing different parts of the job and learning how to do the next part.