Kelly returned from the International Space Station on Wednesday, ending a 340-day mission that set a US record. It took him a full day to get back home from the landing site in Kazakhstan to Houston. That's when the aches and pains set in.

Astronaut Scott Kelly spent 340 days aboard the International Space Station, longer than any American astronaut. Credit:Washington Post

The 52-year-old astronaut said because his skin hadn't had significant contact with anything for so long - in space, clothes just float around you - "it's very, very sensitive. It's almost like a burning feeling wherever I like sit or lie or walk. I'm not wearing these shoes all the time," he said, kicking up his right foot, which sported a shiny black dress shoe. "I just wore them for you guys." Thick running shoes are his preference these days - they make his feet "feel a little bit better".

Kelly's companion for the entire space journey, cosmonaut Mikhail Kornienko, 55, is back home in Star City, Russia, dealing with his own adjustments to gravity.

Many of their blood, urine and saliva samples are still up on the space station, frozen. NASA must wait until its commercial shipper SpaceX is delivering back and forth again - following a launch accident last summer - to get the scientific treasure trove, hopefully in May. Charles expects it will take the next year to analyse all the data.