Walling isn't backbreaking. It is labour intensive, but it isn't really strenuous work. That's why it is always funny to hear people say things like "Boy, that looks like a lot of work ! " or, " I could never lift those stones and do the kind of work you guys do all day".
People will often come by while were working and actually nod their heads and genuinely feel bad for us having to build walls all day for a living. Here we are enjoying the great outdoors, sun shining, no noisy machinery, no stressful deadlines, not confined to some fluorescent lit office working at some high stress job, just hugging stones all day, getting lots of exercise, making beautiful walls that will last hundreds of years, and people are actually feeling sorry for us.
As wallers go I am not really that strong. I generally don't lift really heavy stones. I think with my hands and lift with my legs or with boards or better yet, try not to have to lift them at all. A heavy stone can be rolled into place or simply moved into place with a dolly. If I have to lift a big stone, I don't lift it right up to my chest but let my legs do the work. I can sometimes move a big stone around like this using one hand. Sometimes if a rock is heavy enough you don't need hands at all. Here is one I lifted today. I guess if the stone got any heavier it would just float away!