Photos and videos of astronauts returning from the ISS being taken out of their capsule show them being mostly lifted out by hand and lowered into chairs, where they rest for a little while, then they are taken to what looks like a recovery tent for a little while, then a helicopter ride to a reception center.
By the time they arrive at the reception center they appear to generally have adjusted sufficiently to Earth gravity to walk at least short distances with minimal or no help.
During this short adjustment period of the first few hours, what is it biologically that needs to adjust? A few hours is not enough time to build muscle strength, so this must me at least partly neurological, but is it related to balance (semicircular canals suddenly experiencing 1 g after microgravity for several months) or motor neurons developing sufficient signaling to produce enough muscle power, or the brain remembering how to coordinate, or all of the above, or something else? Has this been studied?