Use it or loose it
Yesterday I got a reminder from Mars! There is a ‘Starmus’ conference going on these days, in Trondheim, Norway. One astronaut told about returning to Earth after 43 days in Space - the message being that what you don’t use (in Space) you have lost when back (on Earth) - i.e. without gravity your sense of balance get lost - you have to retrain basic mobility capabilities upon return. So also for elderly people - without exercising mind and body capabilities get lost....