I'm trying to provide a somewhat realistic explanation of how astronauts were able to overcome the harmful physiological effects of prolonged zero G exposure. As of 2017, issues include: bone/calcium loss (presumably permanent), muscle atrophy, cardio-vascular atrophy and the list goes on to include a few similar health problems.
In my story, the exact date of present day is uncertain, but the reader knows its the future. I simply want address what happened in the interim. I have two ideas so far:
accelerated evolution/genetic engineering, where, assuming a sufficiently advanced lab, the gene for adapting to zero G is turned off. This way astronauts can have normal bone and muscle activity as if under normal gravity and 1 atmosphere of pressure, ect.
Medication, a pharmaceutical 'miracle' drug is administered once a day to reverse the adverse effects.
However I don't want to go too far on the Believable <---> Miracle continuum. Are there any more realistic but still suitable ways to acclimate to zero G?
Zero G Tasks: ship maintenance (internal/external), some parts of the ship don't have artificial gravity. Field science, planets or asteroids having very little gravity.
Duration: Indefinitely, career astronauts on long voyages.