You don't use your arms or back, the weight is lower body, tight core, and balance. I watched my NY trainer carry a very heavy subwoofer down three flights of steps without a problem. I asked him what the secret was- he's not jacked, more lean and his answer was "balance."
I got back to the gym about 1.5 years ago after my Covid hiatus. My balance was horrible. As others have mentioned, weighted squats, deadlifts (under supervision- I use a "trap" type frame, rather than a bar) and core strengthening (planks are good, I find pull ups to be good for that too). I'm not a natural athlete, so I have to work at this. It keeps me lean and ambulatory. I also like the mental effects of a workout. I don't do much cardio, but a lot of the resistance/weight training brings cardio into play. If you lift with your back and you are out of shape, you risk a muscle/nerve pinch type injury which takes a while to recover from. Ask me how I know. :)
FWIW, when I set up my new room after a move from NY to Texas, I hired a couple of big cornfed boys from Texas- the grandkids of a friend. They did the heavy lifting for me. Made life much easier and they were grateful for the dough.