09/19/2013 at 09:00 AM EDT
To portray Formula One racecar driver James Hunt in the new movie Rush
, Chris Hemsworth
had no problem learning how to drive a car zipping at nearly 100 mph. The one thing that scared him the most? Filming his first nude scenes.
"It was more daunting than the racing!" Hemsworth, 30, told PEOPLE at Wednesday's Cinema Society and Ferrari screening of Rush
in New York. "To take your clothes off in front of 100 people and cameras was something I wasn't comfortable with. To be honest, it was embarrassing."
The Aussie heartthrob shows off his buttocks twice in the Ron Howard-directed film and says seeing his tush on the big screen was "odd." But his wife
, Spanish actress Elsa Pataky, appreciated the full view.
"It was more uncomfortable for me to see than her," the Avengers
star said with a laugh. "I think she enjoyed it."
Another challenge for the actor was losing his Thor
muscle. Hemsworth successfully slimmed down and shed 30 lbs. to portray Hunt.
"It was brutal," he admits of working out and not eating big protein meals. "I've said this before, but my wife was pregnant
when I was preparing for the film and I had more symptoms of a pregnant woman than she did. I was hungry all the time and moody."