I'm not sure if can fit perfectly but...
Born on Mars!
With 38% of Earth's gravity, their bodies will grow more, proportionally within the square cube law.
The time for the heart to pump blood to a much larger body and for the electrical signals from the brain go to the extremes will make them have slower reflexes, this is enough to be weak but not so much.
Because they are, well, humans born in different conditions, they have no cognitive differences.
Thick skin can happen thanks to frequent Martian sandstorms.
Being from a world with less atmospheric pressure, hearing and smell are much more sensitive in the Earth's atmosphere.
The difficulty in moving at first in the conditions of the Earth has accustomed us to living in water most of the time, like whales.
Another thing to add: a bigger body will, of course, have a bigger skull and the brain inside will have more room. There is a relationship between neuronal density and sleep time. Since these giants will have roughly the same 16 billion neurons in the prefrontal cortex but have a much larger surface area to distribute them, they will have a much shorter sleep time. Unless they are short of food.