That's exactly how I used to think too! Please be careful.

While your muscles still work wonders, you can be wearing out key points like your vertebrae, facet joints and causing H on your disks and wearing out your joints. Once you damage a part that involves your nerves, which control your muscles...it can be game over.
It fascinates me to no end when I've done too much, how it doesn't matter how much I concentrate on my right foot to make it work and raise my toes, that I can't. I hurt my right elbow this spring when I slammed the door to this house to get it to close. Now I guess I damaged my left elbow last month washing things to be placed back in the porch. Which is so silly, because I wasn't doing anything different, just more that particular day. Now I've lost my pinky finger to numbness and it's moved to the next finger and up my arm to my elbow.I consulted the doctor the other day when I saw her and she said it could be from my elbow. I'm hoping it's from that and not from my cervical vertebrae as the doc also mentioned.
So definitely keep strong and keep from rusting...but don't prematurely wear other parts out in the process. (Take it from someone who's done that)
I can see myself doing that if I was younger and had to stack wood.

When we first got married, we hayed at my Grandparents place and went weekly for a load of square bales for our horses. I loaded Dh's little Chevy S10 just like that.
When we go shopping I am the "master stacker packer" It's my "other" alter ego. It's like the loading of the dishes in the dishwasher, it's like a puzzle.
Maybe I should just do a normal puzzle instead.