Aerobics isn't just dancing and sweating to a fast beat anymore.

Facing declines in participation, fitness instructors are spicing up their acts. They're adding exercise bikes and weight training to the choreography, hoping to gain participants.

The evidence that fewer people are doing aerobic dancing was contained in a survey by a demographics firm.

American Sports Data's analysis of questionnaires from close to 18,000 Americans found participation in high-impact aerobics was down 8.2 percent in 1995, low-impact was down 3.3 percent, and step aerobics was essentially flat at a .3 percent gain.

Aerobic dancing still has a strong base.

The survey found that 10.5 million Americans ages 6 or older had done high-impact aerobics at least once in 1995. More than 13.7 million had done low-impact, and 12.6 million had done step aerobics.

High-impact aerobics requires more forceful movements and is harder on the bones and joints than the low-impact version. Adherents of step aerobics, in which participants step up and down on a low bench, say that activity is less jarring than high-impact aerobics.

Although industry leaders and instructors think aerobics is still doing well, they continue to look for new wrinkles.

"In general, no longer is our industry `aerobics,' as we were 10 years ago," said Kathie Davis, executive director of IDEA, a San Diego-based group once known as the International Dance Exercise Association. "Over the past five years, we have shifted our focus, away from the aerobics and over to the term `fitness.' "

Aerobics instructors have upgraded their skills and consider themselves fitness instructors, Davis said. Many have moved out of the classroom into personal training, including weight training, she said. And classes have expanded from dance steps to include time on exercise bikes, circuit training with weights, boxing or aerobics in the water, she said.

However, the fitness industry has yet to score a big hit with any of the innovations.

One recent attempt, using a slide board or mat, never really caught on.

"That is one of the areas that did not do well," Davis said. "People get tired of it."

Instructors also are trying out other programs. Among these is aerobic cross-training, incorporating parts of step aerobics, slide work and strength exercise, said Libbie Armstrong, aerobics coordinator at The Health Club of Reston.

And the club in the Virginia suburbs of Washington is trying to draw senior citizens with lower-intensity workouts to a slower beat, Armstrong said.

Traditionally, 90 percent of aerobics participants are women. To expand the market, the club has a program based on sports moves, with simple choreography "that appeals to men who don't want to think of a routine they have to be super-coordinated for," Armstrong said.

Surveys also have found that women are increasingly working out with weights. But Armstrong believes they will stay loyal to their aerobics classes.

"They don't have the same social interaction," Armstrong said. "And they really enjoy the music. They find it more fun than spending time on the machines by themselves."