But the actress, who hits the red carpet with the vim and verve of a woman half her age, said the regimen isn't just to keep up her girlish figure.
"The fact that I have always remained physically active has had a great deal to do with it," she said. "It has kept me centered and balanced emotionally."
She said that she's leaned on exercise, even in the toughest moments, such as when, on her 51st birthday, her husband revealed he was in love with another woman.
Fonda, already a fitness guru with a flourishing workout video empire, hopped on her exercise bike and pedaled for five straight hours.
"The physical pain is nothing compared to what I am feeling emotionally," she said, recalling the pain of that day. "I'm breaking apart."
But the workout, she said, kept her from "going over the edge."
"It was kind of like, 'I'm sore, so I must exist,'" she said.
"I know, in the deepest part of myself, the importance of remaining physically active, even if you're going through a nervous breakdown, even if you're older, even if you have body parts that are falling off, it makes all the difference in the world," she explained. "You can go forward in life in a totally different way if you remain physically active."
Fonda speaks openly about the surgeries -- cosmetic and otherwise -- she has had done.
"I wish I was brave enough not to have plastic surgery," she said. "When I got older, and I've started catching reflections of myself in windows and thinking, 'Is that me? But I don't feel tired!'"
"I wanted to look more like I felt," she said. "I tried to keep it appropriate, but I did it, and I'm not going to lie about it."