It is the dusking of the Age of Aquarius.
And as the generation that wouldn't trust anyone over 30 enters their 60's, the fitness industry is singing "You've Got a Friend" to all 77.5 million of them.
"Baby boomers are a booming population. Their numbers are expected to increase by about 25 percent in the next eight years," said Kara Thompson, of the International Health, Racquet and Sportsclub Association (IHRSA).
Boomers span ages 43 to 61, approximately. With the U.S. Administration on Aging reporting that 77 percent of all financial assets in the United States are held by those 50 and older, it's like the poet said: "You don't need a weatherman to know which way the wind blows."
Thompson said an a survey by IHRSA, which promotes fitness through education and sports club membership, showed that gym membership among the 55+ group in the United States jumped from 1.5 million in 1987 to 9.9 million in 2007.
"It is estimated that in this year alone, Boomers will spend over $70 billion on ways to stave off the aging process," she added.
As we age, tendons and muscles shorten, bones lose calcium and lungs lose elasticity, writes Dr. Vonda Wright, in her new book, "Fitness After 40."
But that's just the bad news.
"Only 30 percent of aging is genetic," Wright, who specializes in sports medicine, explained. "That means that 70 percent of how we age is determined by the decisions we make."
Strong spirit, weakened flesh
Boomers have grown up with fitness. Charles Atlas extolled body building in their comic books. Jack La Lane performed jumping jacks on their black and white TVs, and Jane Fonda exercised on their VCRs.
So with the spirit still strong but the flesh somewhat weakened, what's the Woodstock generation to do now?
Wright is specific: "We need 30 minutes of brisk aerobic exercise three to five times a week that gets our heart rates up to at least 70 percent of maximum, daily stretching, three days a week of resistance training and daily balance training." she said.
Fitness centers have heeded the call.
Curves is the leader of the pack. The Texas-based chain of health clubs was founded in 1995 to bring 30-minute circuit training to women of a certain age.
"These women have the most purchasing power of any segment of the population. They don't want to sit their golden years out on the sidelines — more than any other generation they want to stay young and fit," said Becky Frusher, spokeswoman for Curves, adding that it has 10,000 locations in 70 countries around the world.
As more and more over-50's turn up in fitness classes everywhere, teachers and administrators are happily accommodating them.
Programs geared to seniors
At a Bally Total Fitness Center in Brooklyn, New York, instructor Kathy Rubinstein leads a group of mostly baby boomers through her strength class.
"My classes aren't meant for any special age group, but I give variations of the workout. I show them the high impact move and then the low impact move," Rubinstein said.
"I think it's fair to make the workout beneficial for all age groups, so they're not intimidated from taking my classes," she added.
So what can boomers look forward to further down that long and winding road?
Several fitness-club chains in the United States, including Gold's Gym, Bally's, and the YMCA, offer programs specially geared to seniors. The biggest, Silver Sneakers, is in all 50 states and 9,000 locations. It is even covered by some Medicare-based health plans.
"It's an awesome class and a lot of fun for that age group," said Rubinstein, who is 31.
The times, it seems, are still a-changin'.