In Waterloo, Chris Hadfield has his final stint as a lab rat For Chris Hadfield, the return to Earth - scientifically speaking - didn't come last May when his capsule bumped down on the Kazakhstan steppe. Rather it came on Tuesday afternoon while he was lying on a cot in a small lab at the University of Waterloo. With sensors on his arms and legs and an ultrasound probe pressed against his neck, Colonel Hadfield was no longer being tested as a subject feeling the effects of a long-duration spaceflight. Instead it was the degree to which his body - specifically his circulatory system - has regained its former condition that was on display on an array of monitors surrounding his spare, muscular frame. Standing nearby was Richard Hughson, a physiologist and professor at the university who, along with his team, have made Col. Hadfield's blood vessels their focus of study because of the apparent link between weightlessness and cardiovascular aging. "Spaceflight is the ultimate sedentary lifestyle," Dr. Hughson said, "and we know that being sedentary on Earth advances the progression of cardiovascular disease." The last time they peered into Col. Hadfield's bloodstream he was just back from the International Space Station and his body was still entirely adapted to life in free fall. This week Dr. Hughson had his first chance to explore the new "one-g" Hadfield, who has, for the most part, bounced back after experiencing five months of "zero g" while in orbit. The question is whether his arteries have too. Dr. Hughson has examined eight astronauts in this particular study and the results have already confirmed his suspicion that a prolonged stay in space causes arteries to stiffen in a way that is analogous to aging. But his re-examination of Col. Hadfield months after returning, a first for the study, opens up new possibilities for understanding why the stiffening occurs in the first place, and to what degree it is a temporary or permanent consequence of flying in space. "The answer is we don't know yet, which is the exciting thing that comes out of this," Dr. Hughson said. Col. Hadfield's close association with the University of Waterloo, where he will be an adjunct professor of aviation starting next fall, helped create the opportunity for a stop by Dr. Hughson's lab. For the most part, Dr. Hughson has gathered his data by making house calls in Russia or Houston, wherever working astronauts are based. As cameras flashed and researchers hustled around him collecting data, Col. Hadfield lay calmly. On the space station, he said, he and his fellow astronauts would be the ones doing the hustling. "You're both the lab technician and the lab rat," he said. We do it all. Though the afternoon may mark the end of the lab-rat phase of Col. Hadfield's career, he'll continue to be a subject of the team's research for some time to come. Dr. Hughson said that he is still awaiting the return from orbit of some of Col. Hadfield's blood samples that did not make the trip back with him. One of the goals of the research, Dr. Hughson said, is to discover whether any compounds that show up in an astronaut's bloodstream during a mission can be used as markers to track the health of a non-astronaut's arteries as he or she ages normally on Earth. If the work breaks new ground it will be the most tangible return on the 35 hours of lab time Canada was allotted on the space station this year. Now that Col. Hadfield is joining the faculty at Waterloo, Dr. Hughson said he was hoping for another return on his experiment: by inviting his most famous subject be a guest lecturer in his class. When asked at a news briefing earlier in the day about his metamorphosis into a space celebrity, the soon-to-be Prof. Hadfield replied, "I'm still a man of science. My fundamental reason for doing all this is to understand and to communicate a shared interest in how things work. If that's celebrity, then I'm all for it.