We heat our home primarily with wood. Gas furnace for those days when the fire goes low and it's really cold out. In harsh winters we'll go through almost 6 cords. Last year was about 3.
I, too, enjoy the activity of firewood gathering and processing. I use a chainsaw to cut it and a splitter to split it. The only real weight lifting type exercise I get out of it is lifting the wood onto the trailer to bring it home, or tossing it off the trailer when I get home. Then lifting it onto the splitter.
I don't get much weight lifting type exercise tossing or stacking the individual pieces of firewood, as they are so light.
I'd think splitting by hand would do more damage to my body from the extreme shocks of sudden impacts from the maul, sledge, axe, etc., than benefits from lifting weights.
With that said, I still enjoy the process and being outdoors.