The fitness guru – who inspired the nation to "feel the burn!" in the '70s with her at-home workout videos – decided to host the event to promote "the fun and value of exercise," Fonda tells PEOPLE. "It can be a determining factor in the quality of your life and it's never too late to start."
More than 3,000 participants will have the opportunity to sign-up for work-out sessions that range from aerobics with Richard Simmons to tae-bo with Billy Blanks. The event will also be available live online via ustream.tv.
Fonda calls the event "a nationwide call for fun and fitness" for people of all ages. "I am 72 years old," she says. "I've had hip replacement and a recent knee replacement and I am interested in bringing boomers and seniors like me into the exercise world because I know it will enhance their lives."
World Fitness Day will benefit the non-profit Georgia Campaign for Adolescent Pregnancy Prevention, which Fonda established in 1995. Register or get more information on the G-CAPP site.