"It didn't make me laugh because we were just in awe of his abs," she tells PEOPLE of filming the scene. "It got quiet on the set there for awhile."
Hemsworth, 31, stars in the Vacation reboot as Stone Crandall, an up-and-coming anchorman who is married to Audrey Griswold (Leslie Mann) – the sister of lead character Rusty Griswold, played by Ed Helms.
Although the two worked closely together on the film, Applegate, 43, says she remains mystified as to how Hemsworth was able to get into such great shape.
"He said 'I don't really do anything, I just surf,' and I'm like 'that is not from surfing guy. You don't want to give us your secrets? That is not okay.' "
People's Sexiest Man Alive has given Applegate some new goals to aspire to.
"I want to look like Chris Hemsworth when I grow up," she says.
For more from Applegate, pick up the latest issue of PEOPLE, on newsstands now