Surviving in high gravity environment

My son asked me a question about gravity and development that I had no answer for but lots of guesses. I know that the reigning geniuses on this board can help.
Over the years, NASA and the Soviet/Russian space agencies have studied the effects of long term reduced gravity on the human body. We know about bone loss and weakened muscles, etc. But has anyone extensively studied the effect of long term increased gravity on the body?
Imagine you took some rats to the ISS. Their cage is in a centrifuge that will spin fast enough to provide 1.1 g. At 10% greater than normal gravity the rats muscles should strengthen in order to compensate. The bones might thicken as well. If the female rat became pregnant, how would the fetus’ be effected? Would weaker ones be lost or would they just die at birth? Would we effectively be weaning out the weak ones (survival of the fittest)? Could we continue the process for a long enough time and wind up with essentially super-rats that would be much stronger than normal Earth rats? No, I don’t mean they were faster than Speedy Gonzales, more powerful than a rat trap and able to leap tall wheels of cheese in a single bound.
What about 1.2 g? 1.3 g? At what point would the gravitational pull be too strong for the rats to function, let alone procreate?
Thanks for your help.

I don’t know of any experiments, but I can tell you that you don’t need the ISS. You can get whatever gravity you want from a centrifuge, provided it’s more than 1 g, right here on the Earth’s surface. The “floor” of the centrifuge just won’t point straight out; it’ll be at some angle so some of the gravity you feel is from the Earth and some is from the centrifuge.

It’s only if you want a lower gravity that you need to leave the planet.

I’m trying to think of a way for the rats to have a floor so that, for all intents and purposes, the only variable they would experience would be the increased gravity (down would still be down, not at an angle).

Put a weight in the bottom of the cage, and put the cage on the end of an arm that will swivel freely. The direction of perceived gravity will go through the bottom of the cage. It just won’t point directly through the earth’s center.

You don’t even need that. If the centrifuge is to be used at a fixed RPM, you know in advance which direction would be “down”. Just build the cage at that angle.

However, a centrifuge isn’t true gravity. It may be difficult to separate the effects of increased “gravity” from the effects of rotation (i.e. enormous Coriolis force).

The experiment’s been done with chickens; you end up with more muscular, heavily built chickens. I saw it mentioned in Great Mambo Chicken and the Transhuman Condition: Science Slightly over the Edge by Edward Regis. A fun book. And yes, the title refers to the centrifuge-raised chickens.

The coriolis effect will be proportional to the velocities the rats can generate in their daily activities, which shouldn’t be extreme. So it looks to me as if this aspect of the experiment wouldn’t be a big issue.

Thanks for the insight and suggestions. I’ll have to read about the Mambo chicken (sounds like either a variation of Disco Duck or else the latest offering from Applebees).