10 prunes a day should provide plenty of exercise.
I have read the article, and another article linked at the first one. Were people eating these untreated. I have seen packaged “softenized” prunes, and of course you can stew them. Otherwise it might be hard for elderly people with bad teeth to eat an untreated prune. Does boiling them hurt the nutrient content, or canning them? I suppose you could put then in a jar with water and store in the refrigerator for a few days? One would also need to brush teeth to get the sugar off. My Vitamin D, boron and calcium consumption may be doing the same job of preventing shrinkage. At 83 I have shrunk from 5’5”, to 5’3”, but that seems to have been stable for a few years. When my mother was my age she had really shrunk a lot more.