The gravitational impact isn't on the body, but on every molecule that makes up that body.
That is to say that any bodily process that relied upon "heat rises" or any other such basic concept needs to be revisited.
A lighter body wouldn't work out too well: with higher gravity comes higher pressure, with higher pressure comes increased load bearing requirements for any and all parts of the body...not just as regards your own weight, but atmospheric pressure, the ability to move and influence external masses etc.
You wouldn't want to be short and stumpy: leverage is king, the great muscle multiplier.
Massively more powerful circulatory system: It's not enough to recognize that blood weighs 4* as much, the muscles are also doing on avg.. 4* as much work so they need a commensurate increase in delivered payload.
You'd have to redesign the circulatory system almost entirely, because with that 16*(?) increase in load on the heart you're also creating immensely more heat.
Atmospheric density would require reworking the lungs somewhat, you'd have a much higher oxygen content (assuming the average chemical levels are the same across the entire atmosphere) it being significantly heavier than nitrogen.
[with increased gravity the separation between chemicals in atmospheric levels becomes more pronounced/the greater the energy demands are the greater the stratification]
This is a boon for our metabolism, but still not nearly enough to make our lungs sufficient to the task of delivering sufficient oxygen. The best solution...well, hard to say, but I'll tie to:
The energy required for both internal process & external effect will be multiplied, requiring greater resources, but I think it's a mistake to go for "eat more."
See, when we consume (eat, drink and breathe) we don't destroy anything, rather the body transforms one compound to another, creating heat and etc and what the body doesn't manage to use is [largely] dumped out. This is massively inefficient, as the system, when dumping out compounds, could rather use subsidiary processes to reformulate the 'waste' products back into usable forms, separating and re-separating essentially ad infinitum in a closed system.
The whole "tree converts x to y so we can convert y to x" thing can all be performed internal to a single organism, and not just for oxygen and carbon, but for every element and compound required in the operation of the organism.
On the one hand this might provide also a method for using thermal energy rather than extruding it as waste also, on the other this would be even more complex a task than doing the transmutations in the first place, so we might end up with a creature that can't exist at temperatures above -20C or else it would fry itself. So heat management becomes a greater concern than [other] resource management.
The body might be provided with buoyancy devices, not sure how effective such a concept could possibly be, but say.. fluid (as per joints) or hydrogen sacs might help to spread the load or decrease the overall load on the organism's skeleton. I'd imagine that such attempts would require such a volume as to be less than useful, but it's not like I've done the math here.
Really though it seems to me the body would have to be reworked from the ground-up, every membrane has been taken up into the evolved collective because of it's operating characteristics at 1g, quadrupling the energy (not one-shot but permanently) of every particle the membrane is supposed to restrain or redirect is going to have significant impacts.
Assuming normal human babies:
Die as soon as they were forced to rely upon their own hearts.
Muscle density in babies being what it is, a baby wouldn't even be capable of screaming.
Bones would snap even more frequently than adult unmodified humans.
Assuming a child survived birth and magically had a heart and lungs that could operate at 4g, its growth would be immensely retarded.
It would be blind due to suspension deformation in the eye.
Its skull would crush its brain, being too soft and solidifying too slowly to resist gravity's downward stresses.
Liquid where it shouldn't be (lungs) would take that much more effort for the lungs to expel.
Let's talk about weeing and pooping?
Your sphincters are designed to hold materials up to a certain pressure, gravity multiplies downward force, ergo..higher gravity makes you incontinent. Not entirely sure if sphincters would give up 4 times earlier, but certainly they would be under more strain earlier.
Disclaimer: The Above Is All Guessery
I just read some of the answers in "related to" questions and have to reiterate the point that gravity does not act upon the whole of a body, but every constituent particle.
It is not like having to carry extra weight on your back..and not like being a 600lb person. The materials, fluids and molecules in a fat person at 1g behave the same as they do in a regular weight person.
Answers like "wear an exoskeleton" don't help hardly a bit, as instead of being 'crushed' to the floor, you're being 'crushed' into the exoskeleton.
If 'live under water' would help, wouldn't we suppose NASA would of built a huge tunnel up into space filled with water so shuttles could sedately swim to the surface? Gravity doesn't stop exerting its influence just because you're in a suspension.
If we put a put a person in a centrifuge pod full of water and turn it on, for instance, the difference we get is that before the person is crushed to the rear of the centrifuge...the water must be force out of the way. Which takes..no more time or effort than it takes a person to move through water under any other conditions.
Can water be compressed? Does it matter? I don't see how it can matter. Pick up a bath full of water. Pick up a bath full of water under 4G. Submerge yourself under water in 4G conditions and you're dead even quicker than in atmosphere. Every one of those water molecules weighs 4* as much as on earth...you are not water.
Perhaps..turn people into jellyfish.
Babies could be grown in vats in space and engineered to the desired specs before being dropped.
I mean, it seems to me that 24th century man could do it [hell, if people put their minds to it and discarded any misgivings now we could probably find a way and make it happen inside 40 years [that is, apart from actually getting to this planet], but the result couldn't be human by any but the most generous definition.[not that this is a problem, just pointing out my view of the scale of changes required.]