If say we can survive on Mars and there's oxygen and food and water, I wonder what kind of effects will there be on the human body. Since Mar's gravity is weaker than Earth.

we will be able to jump like Tim Duncan.

At a guess, I can imagine future generations might be taller (subject to natural selection).

Digestive and circulatory systems wouldn't work as well since they partly rely on gravity at 1g.

Coordination might become tricky since your sense of balance would be altered.

One major change would be a reduced muscle mass....same as astronauts experience. A smaller and weaker heart aswell probably

IS there a way to reverse the symptoms? Rehabilitation?

Taller, lower muscle mass, lower bone density. Probably larger lung capacity if you want to breathe at anywhere near current atmospheric pressure on Mars.

What if he's like deep underground?