Okay, this is a question that's always kind of bothered me. According to dozens of articles and interviews with NASA employees or professional astronomers, one of the biggest dangers of long term space travel is the bone and muscle loss. That totally makes sense; being in zero G is even worse than laying in bed for months as far as bone and muscle use is concerned. But the thing I don't get is; would that be a problem at all if we weren't planning on returning to earth gravity? It always seems like the only danger that you incur is that you won't be able to readjust to earth's gravity, but frankly in the long term we won't really be worrying about that because we'll have people living on mars indefinitely. Is that true, or are there effects that will kill you even if you stay in a low G environment?