The problem as we get older, is that we have less energy for the day to day tasks and thus there are less reserves of energy that are required for processing the fixes and daily needs, it has been noticable with the new techniqueks of surgery that people have been recovering quicker as they do not need the time and energy that is required for old methods of cutting and dicing. When young we process more food {energy} [ like 5 to 6 times more] than when we are in our eighties [ I do, My Sunday dinner would last me 5 days now, thank goodness, I no longer have the money to feed the old me] Then the rehab requires ooodles of energy, and so we steal it from other functions they then fail do to the lack of energy.