Scott Kelly's year in space will go down in history as one giant leap for mankind's space exploration.
However, now that the NASA astronaut has returned home there are quite a few adjustments his body will have to make to living on Earth.
Scott Kelly reacts after landing on Earth
Here are five simple things we take for granted that Kelly will probably find difficult to deal with.
Spending a year in a weightless environment can make standing upright on Earth quite difficult. While the process does take some time, NASA uses this change to study how the human body responds to a "long-term, low-gravity environment."
When in space, astronauts lose up to "1.5% of their bone mass for each month spent in space," writes Robert Frost, instructor and flight controller at NASA, on Quora.
The loss is greatest in the upper thighs and pelvis, he explains and while the bone will regrow, this period of reduced bone mass can place the "astronaut at greater risk for injuries such as hip fractures".
While in space, Kelly's heart would have also undergone changes as it did not need to work as hard to pump blood around his body,
As a result, his blood pressure will be significantly lower causing dizziness and disorientation if he stands up too quickly.
When retired astronaut, Chris Hadfield, returned to Earth in 2013 he reported having to change the way he talked.
"Right after I landed, I could feel the weight of my lips and tongue and I had to change how I was talking," he said, according to Space.com
Speaking at a press conference at the time, he explained:"I hadn't realized that I learned to talk with a weightless tongue."
Becoming younger and older at the same time
One of the more well-known aspects of Kelly's journey is the comparison that is being made to his identical twin brother Mark Kelly, a retired astronaut.
Since Mark stayed on Earth, the pair have given scientists an incredible opportunity to make a more direct comparison between two humans who are genetically identical.
One key change already observed is that Kelly has aged less than Mark, who is older by six minutes.
Speaking to the Guardian last year, Mark said: “The effect is known as the twin paradox, though it is not actually a paradox, it is a straightforward consequence of the laws of relativity."
He added: “Essentially, time will pass slightly more slowly for Scott than for me because he will be travelling at a greater speed relative to me.”
In terms of time, Kelly gained 25 microseconds a day, which amounts of 8.6 milliseconds over 342 days, Quartz reports.
However, this probably won't compensate for his body ageing more quickly in terms of biology.
Moving your neck
Since bones and muscles are still weak, astronauts have reported straining their neck by turning too quickly.
Full bone recovery, after returning to Earth, takes between six months and three years according to Frost. It all depends on physiology and age.
Spaceflight can negatively affect eyesight.
Research in 2012 studying the eyes and brains of 27 astronauts found that they had abnormalities similar to patients who have a condition where pressure builds up in the brain, Space.com reports.
The reason for this has everything to do with gravity. When in space there is a redistribution of fluid, which increases pressure inside the skull.
One possible reason for this could be that one of the outlets for this fluid, presses against the optic nerve, pushing back on the eyeball.
In a press conference Kelly noted that his vision had changed during his year in space, The Verge reports.