Gravity is not a pinning force. We, as living beings, have internal rotational fluid dynamics within our muscles and within our system in general. This rotational interaction functions in accordance with the gravitational field of the Earth around us. When we leave Earth's gravity, our system no longer functions with this internal rotational gravitational balance. Our system looses this functionality and that is why astronauts returning to Earth have to relearn how to function in its gravitational field.