If humans could travel to Jupiter...
You mean inside the atmosphere?
Unfortunately, since Jupiter's atmosphere is made of the lightest gases, it is practically impossible to get a balloon to float there. The combination of gravity and pressure also means that we simply do not know how to make a plane that would be able to fly in there indefinetely. To fly there for even a few seconds would involve aerobraking a flyby, which is suicidal.
Let's suppose this is handwaved away, and that you'll use a pressurized habitat. Jupiter's surface gravity is 24.79m/s2, roughly 2.5x that of Earth's. Notice that Jupiter has no surface - that is just the gravity where atmospheric pressure equals that of Earth at sea level.
If you search sites like Wikipedia, you'll find that many sources cite untrained people can sustain forces of up to 4 to 6g before passing out, which is more than Jupiter's surface gravity. However, any sharp turn of your jovian vessel could knock you unconscious. Adaptations to prevent this would include stronger musculature and heart, and a brain more resistant to strokes.
I don't have much data about long term exposure to high gravity, but we did some speculation on this other question of mine:
Technological adaptations for colonization of a higher gravity world