Baby boomers were the first generation to make "working out" a lifestyle in large numbers. And as they approach or pass age 50, they haven't slowed their pace.

During the past decade, in fact, fitness has become both a buzzword and a lifestyle choice for Americans of all ages. Fitness centers offer programs for children. Schools emphasize exercise and physical education. Colleges build new fitness facilities as a competitive device to boost student enrollment. And senior citizens, whether they live at home or in group settings, are taking time to exercise."Tracking the Fitness Movement 1987-1997," a special report released by the Fitness Products Council, documents what it believes are the eight major fitness trends of the '90s. And it predicts 12 new trends to which health-conscious Americans will want to pay attention.

-- In the 1970s, we ran. Everywhere. A decade later, aerobics ruled the fitness world. But the 1990s have become the "Machine Age," according to the council.

Machines that provide cardiovascular workouts, like treadmills and stair climbers, are the most popular, with strength training machines not far behind. The council estimates that 67.2 million Americans get a machine-assisted cardiovascular workout. At least 49.5 million do strength-training, while 33.2 million walk, 32.3 million run and 22.8 participate in aerobic dance.

-- In 1995, working out with free weights became the No. 1 fitness activity in America. And much of the growth has been attributed to the increase in participation by women, the report says.

-- Treadmill exercise is the only activity that grew every year of the study, increasing 720 percent over the decade. Now 36.1 million Americans 6 and older use a treadmill as part of their regular activity.

-- Americans not only expect a car in every driveway and a microwave in every kitchen. They're increasingly demanding access to health clubs. Fitness facilities have sprung up in apartment buildings, corporate offices and colleges. An estimated 22.5 million Americans have memberships in health clubs and that doesn't count the people who have access to those other gyms.

And not just young adults use them. While the 18-34 crowd accounted for more than half of all health club memberships a decade ago, they now are only 41 percent.

The report says that access to fitness equipment is now a "quality of life factor."

-- Growth of fitness facilities is nothing compared to home health equipment sales growth. Consumers spent $2.68 billion on it in 1997. And the Fitness Products Council claims that exercise equipment is used in almost one-third of U.S. households.

-- As mentioned, baby boomers continue the fitness trend they started.

-- "Innovation is a hallmark of the fitness movement," according to the report. Arrivals and departures on the fitness scene in the past decade have included stair climbers, abdominal trainers, aerobic riders, cross-country ski machines, aerobic gliders and elliptical motion machines.

Group aerobics have changed, too, from high-impact to step aerobics to body toning. Now it includes yoga, ethnic-dance movements and classes around equipment such as bicycles, free weights and treadmills.

-- Stars and sports figures aren't the only folks with personal trainers. In 1993, the Aerobic and Fitness Association of America held 96 certification workshops for personal trainers. Last year, the number was 288.

The report also looked at why people exercise and found that the answers depend on your gender. The top three reason women exercise is for weight control, because they feel good after exercise and for increased energy. Men, on the other hand, list muscle tone, increased energy and cardiovascular benefits as their top three reasons.

While the numbers of people exercising are up, a lot of the increase is due to population growth. The report warns that lack of physical activity is till a leading health problem in America.

According to the council, fitness participation will "continue to grow faster than the population over the next three to five years." Reasons it will increase include vanity, desire to delay the aging process, better information about the benefits of exercise, use of fitness equipment to enhance the home and the proliferation of fitness facilities.

They expect to see more instructor-lead group exercise that uses equipment, like "spinning." More exercisers will use heart-rate training. And the preventive-medicine benefits of exercise will continue to change how people approach fitness.

The council also predicts that treadmills will remain king of the equipment in the forseeable future, while elliptical training equipment is fast becoming essential to a well-stocked gym.