Previous post is written by a European, I am sure. Europeans I know can without training, do a pull up, or climb a rope using only the hands, or in the old days, lash the topsail to the cross brace in a rainy gale. My body is designed to run down deer with an atlatl until the animal collapses from exhaustion, so sheer upper body strength is something I have to work on. The lower body comes naturally to me, I can still walk 27 miles in 7 hours or bike it in 2 1/3. Playing piano, especially exercise books like Edna May Berman and Czerny, is adequate for building strength in the fingers and forearms, IMHO. It worked for me However my upper arm muscles become quite weak unless I do something continuously. As a youth I carried 20 lb of books and a bassoon home from school 3/4 miles. In my twenties thirties I relied on the Army Daily Dozen, then in the fifties work as a factory mechanic. However, now I notice deterioration in upper body strength especially in the winter, unless I do something. I'm daily doing some pilates exercises with a 5 lb weight for biceps, triceps, deltoids. I learned these off the Margaret Richards TV program. I'm doing pushups leaning against a chair, since floor pushups hurt my wrist badly, and I'm doing situps 1/2 way down instead of going all the way to the floor (I'm age 63). I'm also doing toe touches for my back muscles, since a couple of years ago sitting on the bench for an hour started making my back muscles get sore. I walk and ride a bicycle a lot in the good weather, and do 1/2 hour on an exercycle with pulse between 100-140 in the bad weather. A lot of vigorous piano can still make me elevate my breathing rate.
You can exercise so much you become muscle bound, as a friend did. He was so strong and chuncky from exercises promoted by his karate instructor, that he couldn't pass the US Army PT test due to poor flexibility. So if you want to be pianist, don't overdo it. However, most US residents are blobs of fat waiting for their first heart attack, so definitely some exercise is in order unless you heat your house by chopping wood and feed yourself by cultivating with a mule.
Also, from age 14 to 50, male testosterone will cover up the damage you can be doing to your joints, which will haunt you age 55. Many formerly pro atheletes are chunks of flab in their late fifties onward because movement hurts so much. So make sure your exercise is not excessivly kinetic on the joints. Bottom line, live like your great grandparents, however artificial the exercises are, IMHO, and you will be fine.