Another thing we just don't know, is whether it is good enough to have
limited exposure to 'g' to overcome the deficits of long duration in 0g
or low g. Thus it becomes routine to spend some time working out in a
centrifuge and the rest of the time in 0g or Mars gravity or whatever.
Call it extra-terrestrial PE....

I remember the classic video of one of the Skylab astronauts (was it
Conrad?) getting their exercise by 'running' around the inner
circumference of the Skylab habitation module.