I would always chuckle when I would see some city faggots at a gym hitting an old tire with a sledgehammer for a workout. They're paying to do what they could do for free at my place with a block splitter and a big pile of firewood.
Lifting rocks though is a really good way to work out. You should lift the heaviest rock you can (without injuring yourself) only a few times. The irregular shape and weight distribution of a natural rock works out a broader range of muscles. Lifting a very heavy rock induces hormesis, basically tiny injuries which trigger the body to reinforce that area of muscle and/or bone.
I used to train for years in an old school boxing club. We had a tractor tire and a makeshift heavy wooden club. The idea was to hit the tire as many times as possible, as quickly as you can until you nearly black out. It was meant to build stamina. Then some crossfit faggot probably saw boxers doing that and thought it was meant to grow your lats or whatever.
If you used a sledgehammer with force that we were hitting that tire with, it would break after the first use.