Trainability of body parts

For a long time I've had the notion that some parts, or organs, of the human body can be trained to function better, be stronger and more disease-resistant, while the others cannot. The heart and the lung can be trained by aerobic exercises, or made stronger by eating dark chocolate, or drinking a small amount of red wine. Muscles of course can be trained to be stronger, and by the same exercise for muscles, bones can be made denser, less prone to fracture in old age. Even the brain has plasticity, so that cognitive ability can be improved with seemingly monotonous drills such as learning to play the piano, or logical thinking such as playing crossword puzzles, or learning a foreign language.

On the other hand, most organs of the body cannot be trained. You can't directly train your stomach to have better digestive power, unless you improve your health in general, which indirectly improves the function of the stomach. (Chickens eat pebbles to help digest, which may be the way they directly train their stomachs. But humans are not chicks.) The liver cannot be trained. Can you drink a modest amount of wine every day to improve the function of the liver, in the same way immunization works? As far as I know, even a tiny amount of alcohol is harmful to the liver, although the little harm may be outweighed by the benefit to the heart and blood vessels.

Surprisingly, whether an organ is trainable is or will be identified unambiguously, a clear yes or a clear no. But there's more to it. An old Chinese doctor on TV claimed benefit of moving eyeballs. I always thought eyes belong in the untrainable category. But he says his good eyesight is due to his daily eye exercise, including rotating eyeballs counter-clockwise dozens of times, and then clockwise (with eyes closed), followed by kneading a few acupuncture points around the eyes. Unfortunately, like almost any TCM doctor, he has not done any controlled test, which is the gold standard in modern medical science. While I still believe an organ is either trainable or not, as time goes by, more organs may move from the untrainable to the trainable. Brains used to be thought to be fixed and rigid around age of 10 or younger. But discoveries in neuroplasticity throw doubt on it. Eyes may move to the trainable group in the future, and we're expected to prolong the onset of near- or far-sightedness, macular degeneration, glaucoma, etc.

I have yet to find published materials discussing this classification of human organs. Unless it turns out that all organs are trainable (or all untrainable), I believe this classification will prove to be a useful concept in health science.