When the cost of putting people on Mars drops to an affordable range, there will be no shortage of people wanting to go there to build a new world: Life on Mars to become a reality in 2023, Dutch firm claims: Thousands apply to become one of four astronauts selected to set up a human colony in a plan that comes with snags – guardian.co.uk.

Regarding the effects of living for a long period in gravity that’s 38% of that on earth, we don’t know the effects. The only data on fractional gravity is from the Apollo astronauts that spent a few days on the Moon and this was too short a time to have any effect.

To answer such questions, the Space Studies Institute has proposed the G-Lab, a rotating tethered habitat system for doing long term animal studies at different gravity strengths.

For a Mars settlement plan, it is not unreasonable to make the working assumption that it would be too dangerous to attempt to re-adapt to earth. However, my guess is that it will in fact be quite possible for a long term Mars resident to adapt to Earth’s gravity. The fundamental physical capacity to withstand that level of gravity will remain and can be retrained.

Ultimately, it would make sense to have a transport system traveling from Mars to Earth to provide rotation to generate spin gravity. This would allow for the gravity to be gradually increased from 0.38g to 1.0g over the course of the months long trip and allow passengers to gradually adapt to Earth conditions.