While Jennifer Aniston's bangin' bod has been the envy of many for years, there's no doubt the 45-year-old stunner works incredibly hard to maintain her super-fit figure. The former Friends star is currently celebrating fiancé Justin Theroux's 43rd birthday—which also marks the couple's two-year anniversary—with a romantic vacation in Bora Bora.

So how does Jen stay in shape so she can sport those two pieces like pro? Celebrity yoga instructor Mandy Ingber spoke to ABC News and opened up about the actress's fitness routine, admitting its all about amping up the cardio when Aniston is looking to "trim down." "Jen's a very consistent exerciser and eater," Ingber said. "But when she has something she needs to focus a little more on, she just tightens it up a little bit."