"I'm part of a demographic that's kind of ignored. We have to go into it with guns blazing and be as healthy as possible," said Fonda, whose first exercise video "Jane Fonda's Workout," released in 1982, remains the top-grossing home video of all time.
"Every aspect of your life will be better when you're older if you remain physically active," she said.
Fonda will be joined by a slew of celebrity trainers including Richard Simmons, Denise Austin and Billy Blanks. The celebrity trainers will lead an hourlong group workout expected to draw more than 3,000 people to the Georgia Dome. Those not in attendances can follow along with the workout online via ustream.tv.
"I'm right after Jane Fonda and she's doing the warm-up, so I want to gradually get up the pace a little," said Austin, a pioneer in the exercise industry who has sold over 20 million exercise videos. "We're here to say come on you can do it, you are worth it, you deserve to look and feel your best."
The festivities will also include performances by rapper and actor Chris "Ludacris" Bridges and The Pointer Sisters. California Gov. Arnold Schwarzenegger will also deliver a video greeting.
Fonda, also a two-time Academy Award-winning actor, says new hip and knee prevent her from strenuous workouts, but she always finds a way to stay active.
"Just do it. I don't particularly like working out, but i'm motivated to do it because of how I feel afterwards," she said.
Proceeds from World Fitness Day will benefit the Georgia Campaign for Adolescent Pregnancy Prevention, the nonprofit organization Fonda founded in 1995.