Prolonged exposure to low gravity in the ongoing space programs has yielded surprising results on the bodily effects. Nobody has so far managed prolonged exposure to high gravity - quite possibly, surprises might await us there as well, and a human sent to live on a world of 1.05 G would be doomed to a horrible death within months.
On the other hand, our heroes are beneficiaries of highly advanced medical science. It might be that they have been engineered not so much to cope with high gee or low gee, but to be more robust overall. And not by making the organs better, but by switching off a few genes so that their bodies don't adapt to the gravity changes in any manner and thus don't do harm to themselves.