I'm not sure... it depends on what the point is where the human heart is no longer able to pump blood effectively. Anything under that point I suspect would be liveable, but it would definitely be difficult to get used to. I also suspect that unless there was some way to train for increased-gravity conditions, people would be injured trying to adapt, again depending on the increase in gravity. Also likely is that it would decrease lifespan, or at least physical wear on the body. Look at someone who has done manual labor for most of their life, and compare that person to someone who has worked a desk job for most of their life. The laborer will look much older and worn out. I suspect that the constant stress on the body would have a similar effect... humans have evolved to the gravity on earth, and changing that can have bad effects. Look at people in zero-G; they have to work out quite a bit, so their muscles don't degrade too much. We're talking about the opposite effect really: too much gravity damaging the muscles and body.
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I'd rather be climbing...
I approach college much like a recovering alcoholic--one day at a time...
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