It may seem obvious, but I think it’s important to remember how hard physical work is.
In a modernized world, it’s easy to take granted things farming, mining, construction, or even more mundane activities like mowing the lawn or cleaning the house. But we have been doing physical work since the beginnings of human history.
Physical work dignifies and envigorates; there is something about it that is different from say, training or working out. Seeing the final product and get tired at the end of the day seems a bit of a reward in itself.