My theory on exercise is that it's overrated. Look at Stephen Hawking - he didn't get much exercise for the last fifty years of his life and he lived to 76, which isn't bad. Look at people lying in nursing homes who don't leave their beds for years. The difference - those people don't eat whatever they want. They are fed by a tube, get weighed, and their institutional diets adjusted accordingly. So diet is probably more important than exercise in preventing sludge buildup.
But if you want to do something besides lie in bed all day, or if you want to walk instead of having someone push you in a wheelchair; if you want to climb a mountain or paddle a canoe, fitness is important. And if you want to avoid injury, you work your way up to it gradually.
