In article ,
says...

I have a feeling that something like this has been done with animals, after
all you would not really want to be messing about with your crews welbeing
in this way. I was interested in the reasons for not doing the camp out any
more before EVAs and using excercise to help remove nitrogen. one supposes
this must be safe but its a bit risky I'd have thought as long term it
might give rise to issues. Maybe this is why not that many us evas are
planned.

You guys have heard of Skylab, haven't you? If I remember correctly,
even though it was an O2/N2 mix, it's internal pressure was far less
than sea level. A quick web search says:

According to NASA SP-400, "Skylab, Our First Space Station," the
atmosphere was 74% oxygen and 26% nitrogen at 5 psi.

In general though, NASA feels most comfortable with sea level pressure
in spacecraft, perhaps because that's the pressure at KSC and JSC.
Never mind the fact that millions of people on the planet live with far
less than that each and every day. Denver Colorado experiences about
12.1 psi, which is less than sea level which is about 14.7 psi. Note
that Denver isn't even *that* high in altitude at 5431 feet at the
Denver International Airport.

I've hiked, with a 50+ lb backpack, at altitudes of 11,000 feet which is
somewhere around 10 psi. You do get winded faster than at lower
altitudes, and it takes more time to catch your breath, but it certainly
didn't kill me.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer