"I guess right now this feels much, much harder," Spencer told a US interviewer during the filming of Chicago Fire, which follows the professional and personal lives of the firefighters and paramedics at a Chicago fire station.
"After eight years of being an intellectual and spewing out medical terms, it was time to do something in the opposite direction.
"When I think back to the early days of House, that was really tough, too. We had extremely long days.
"It was tough in the first couple of years of the show. And that's what this feels like at the start of Chicago Fire, except you also have the physical demands."
The preparation period for the show saw Spencer and his fellow actors, including Taylor Kinney (The Vampire Diaries), David Eigenberg (Sex and the City) and Eamonn Walker (ER), undertaking practice runs and fire drills at the Chicago Fire Academy.
While Spencer admits he occasionally messed up during these training sessions, at one stage leading his team of firefighters into a closet rather than through an exit, he says the process helped create a bond between the real-life heroes and the actors portraying them.
"We've really got a rapport because we spend so much time together," he said. "We shoot at the real firehouse once a week and there are other firefighters there, so it's pretty authentic surroundings for us.
"If we've got questions, you can literally turn around and ask the closest firefighter what's up.
"We hang out on weekends, so it's a different scene and a different energy and that's quite invigorating."
One thing Chicago Fire is keen to do, Spencer says, is present a positive but realistic depiction of men and women heroically doing one of the most dangerous jobs there is.
"Our show is more of an inspirational, optimistic view of firefighters," he said.
"Here's the thing: I think everyone loves firefighters.
"Firefighters don't consider themselves heroes but if you look at their job description they are - their job is to straight-up save people.
"We do delve into all sorts of issues [on Chicago Fire] - you see their lives outside of the firehouse probably just as much as you do in - but it doesn't get bogged down in the psychological element of it. It's an hour of entertainment."
It's also Wolf's bid to create a "very classic and adult" ensemble drama in the vein of Hill Street Blues, ER and his own Law & Order.
"It's hopefully in the tradition of these shows that have become, for better or worse, iconic," said Wolf.
And while he calls Chicago Fire "a character study about people who do things you can't pay people to do", he stresses that the characters' lives beyond their work will be explored throughout the course of the show.
And the men and women of Chicago Fire indeed wrestle with relationship dramas, economic issues and other after-hours problems.
Already separated from his wife Hallie (Teri Reeves), Spencer's Casey is then estranged from his friend and colleague (paramedic Kelly Severide, played by Kinney) after a fatality in the show's first episode, with the two men blaming one another for the incident.
"That relationship between Casey and Severide is quite strained," says Spencer.
"But it's not always going to be like that. They're going to find their feet again.
"[But] it really sets up the tension between them. The real firefighters on the set, they've all got buddies they've lost and it's really tough.
"It's a harsh reality to lead the audience into and it's going to put it in their faces that death happens sometimes on this show."
TV preview
Who: Jesse Spencer, Aussie actor, former House doctor, now Chicago firefighter
What: Chicago Fire
When and where: TV3, Tuesday 9.35pm
- AAP
