Roscosmos, Russia's federal space agency, proposed that NASA missions increase the length of stay on the ISS from six months to nine months and eventually to extend the stay in orbit to one year.
Longer stays would require significantly more rehabilitation on return to Earth, experts said.
"We know how to rehabilitate astronauts [after a long duration space flight]," Roscosmos head Vladimir Popovkin told RIA Novosti. "For Europeans and Americans, the problem is harder, they do not have this experience. ... And so we are ready to use everything we know to help, perhaps, to change the rehabilitation period of [foreign] astronauts."
Foreign astronauts usually return to their home countries directly after ending their ISS missions, which can sometimes cause problems for them, Popovkin said.
"After such a long space flight, a normal flight home is a big problem," Popovkin said. "Maybe they should fly here [to Russia] for the first two to three weeks for an extended rehabilitation period."