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This answer suggests that outer planets are very heavy and that lifting things on it is very energy expensive.
If someone was to workout on a planet that is considered 'heavy' (whatever that means) would they have super strength once back on earth? (Think DBZ and goku training under heavy gravity.)
So, what are the effects of body building on a heavy planets?
No, you wouldn't become a superhuman. Well, at least not for the workout part of this endeavour. Essentially, every mass object would be heavier due to stronger gravitational pull of a larger mass planet than Earth. Say, you use weights to exercise on these gas giants the question you're referring to is inquiring about. And let's, for the sake of argument, pretend you are protected from all the environmental hazards of being on (in?) such planets, and you actually have somewhere to stand (gas giants like Jupiter and Saturn don't really have a solid surface, so you'd be suspended at a point of equal atmospheric density than the average of your own body and whatever you carry on your person, and ice giants like Uranus and Neptune, while they have a solid surface, it is at a depth of a rather uncomfortable atmospheric pressure).
These weights would become heavier by weight, while their mass, of course, stays the same. Something you can do just as well on the good old Earth by simply using heavier weights in the first place. To be more accurate, this gravitational pull wouldn't work on weights only, but on your body as well, so even lifting your arms would involve a lot more effort on its own. You could simulate this by attaching additional weights to your limbs here on Earth, for example. Or doing weight lifting exercises while submerged in water and account for weight difference in displaced water (buoyancy) by using heavier weights.
For example, Jupiter's equatorial surface gravity is 2.528 g. g stands for g-force, or a measurement of acceleration felt as weight. This means that the 10 kg weights you'd take from Earth with you to the Jupiter would weight there roughly 25 kg. You, the man doing the exercises with these weights however, still have the same physical strength, your bone structure can support same amount of stress (if you didn't spend too much time in zero-g travelling there, and your cardiovascular and respiratory systems can take the added strain and you don't simply collapse due to G-LOC induced hypoxia, heart or lung failure once at the hypergravity environment),...
In short, you would probably feel stronger upon your return (not taking into account your travel back to Earth that would mostly be in zero gravity, negating any such positive effects from before, like muscle atrophy, bone loss, and so on), but that's something you can try e.g. by using a heavy training basketball for a few minutes, and then switching back to a normal one. The normal basketball will appear to "fly" off you as if it was featherweight. Well, for a few minutes at least, until you "recalibrate your senses". Either case, you could practice in becoming a superhuman in a lot safer environment than gas giant outer planets.
Thinking the effect when an astronaut comes back to earth from long time exposure in some low gravitational environments, the lost bone density won't be immediately regained. He/She faces greater chances of fracture.
I believe human will face similar situation when going to a relatively high gravity planet. You will face higher chances of fracture, but gradually your body will adapt. Eventually you will gain higher bone density and better muscle strength (like workout with extra weight).
There is a limit to how fast humans can build up muscles. Body builders choose weights and exercises to put their muscles under the ideal strain for muscle growth. The art of body-building is to find that ideal level for each muscle which neither under- nor overstrains it. A different gravity would mean that
That means that in a higher gravity, exercises will be more straining than in earth environment. That means that their usual training plan would be far too intense and they would just injure their muscles. The athlete needs to decrease the intensity of their training plan to get the strain back to the ideal level. That means a body builder could not achieve significantly more progress in a high-gravity environment.
However, when you would put a normal person in a high-gravity environment who does not consciously exercise, they would likely still build up muscles. The reason is that every-day tasks put more strain on their muscles than on Earth. Eating a meal with a fork could be equivalent to a workout with a barbell and a leisure walk to another building would be like running up a mountain. But the effect is unlikely to be better than with a well-planned intensive training program on Earth.
It might be a bit of a surprise, but only two of our outer planets actually have higher surface gravity than Earth - that is Jupiter and Neptune, and Neptune is only 12% higher. Saturn and Uranus, although much heavier than Earth, actually have lower surface gravity because of their very low density, this puts the surface much further from the center of mass than in the case of Earth, and is sufficient to result in lower surface gravity.
Note that although they have lower surface gravity, the escape velocity is still much higher than Earth's. A way to look at this is that the gravity well is "deeper" but isn't "steeper". Also even though the gravity is weaker, the required velocity for orbit is still higher - the required orbital velocity to offset the centripetal force of gravity is proportional to the square root of the orbital radius, Uranus has 4 times the radius of Earth, so at "LUO" just above Uranus's surface orbital velocity is twice that of Earth LEO, and so getting into orbit requires 4 times the energy.
So surprisingly enough, at least for two of the heavy outer planets, it's actually an easier workout for a weight lifter - but it's still much more expensive to lift things off the planet.
Ultimately, human strength is not limited by the amount of muscle mass you can build, but by things that don't grow as much (tendons, joints). So a human who's born on Earth and goes to a high-G planet to train for a few years will not become stronger than his peers who've been training on Earth.
What I suspect would make a difference is living on a high-G planet for a number of generations. The body will adapt to changing circumstances, so eventually you'll see humans born on a high-G planet becoming stronger on average, and being able to reach a higher peak strength.
There'll be some interesting side effects to training on a high-G planet. The heart will have more trouble pumping blood 'uphill' to the brain, for instance.
Yes, you would become a superhero. It's nowhere stated that heavy planets should be gas giants, there are heavy outer planets with hard surface. And like effects of micro gravity are measurable (muscle atrophy), so would be effects of hyper gravity (muscle hypertrophy and consequentially higher bone density). Every move would become exercise and there is little overall Earth training that could be compared to that (except maybe swimming). If carried incrementally it could work like in Dragon Balls.
