It started like an ordinary yoga class.

The instructor dimmed the lights, turned on soothing music and began to lead the small group in breathing exercises.

Then she instructed them to go “into cocoon,” and all three of them wrapped themselves in nylon fabric suspended from the ceiling. Over the next hour, they barely touched the floor again.

Kaya Aerial Yoga, located in a former carriage house nestled in the Old City section of Philadelphia, uses lengths of fabric called silks, or hammocks, to suspend participants above the floor while they exercise.

Aerial yoga has taken off in the past couple of years, but its roots are in AntiGravity (a registered trademark), an aerial fitness program created almost 25 years ago by Christopher Harrison, a dancer and gymnast who does aerial choreography for Broadway shows and other productions.

The Future Fitness Powered by AFC gym in Cherry Hill uses another brand, VaihAyasa Aerial Yoga, for its classes. Lucy Kemp, one of the aerial instructors at Future Fitness, discovered aerial yoga seven years ago and lobbied to make it part of the gym’s class offerings.

The silks help people to get deeper into positions and increase their flexibility, Kemp said. It challenges the core but also provides a safe, low-impact workout.

The nylon fabric can support up to 1,000 pounds, fastened to the ceiling with mountain-climber-certified steel rigging.

“It’s another tool,” Future Fitness instructor Kate Christopher said about the hammock. “It gives you the opportunity to get extra support and then use your body. It’s a whole body workout. Your arms, your neck, everything gets involved.”

Using the silks as added support can help people build strength slowly and take pressure off joints.

“You’re taking anywhere from 50 percent to 80 percent of your body weight away,” said Kaya owner Carrie Ann Felinczak.

The silks also help aerial participants achieve proper balance and alignment, said Sara Filseth, another instructor at Kaya. Filseth has some back problems but said aerial yoga has helped.

“It is very therapeutic,” she said.

Felinczak discovered aerial yoga after suffering from a painful nerve condition for a decade.

“When I was in college,” she said, “I had a car accident, and I went through the windshield and had a crush injury.”

For the pain, doctors suggested yoga, but floor yoga didn’t help her. Neither did acupuncture, painkillers, nor anything else she tried. She eventually discovered the Kaya studio, then under different ownership, and took a class.

“It was the first night I was able to sleep and didn’t have pain,” Felinczak said of that first class. She and her fiance eventually bought the space and relaunched it this past summer with a large roster of classes including intro classes, Pilates-based conditioning, circus, dance and boot camp.

There was a point when she thought she might not be able to climb stairs anymore, she said, but now she is training in dance and circus aerial styles.

“I would never be able to dance on the floor again,” she said, “but being able to learn it in the air is amazing.”

At both Kaya and Future Fitness, classes are small and individualized, so the instructor can take everyone through the moves safely and adapt positions to each person’s skill level.

“You can have a group of people who are all different fitness levels taking it,” Kemp said.

Kemp also added that, although many participants are women, some of the male gym members also come to the aerial classes.

Future Fitness also has a range of classes, from restorative yoga to boot camp-type classes. There are three intro classes every week, where beginners learn the basics of working with the silks.

“Some people are hesitant to try it,” Kemp said. “They look at it and think, ‘I can’t do that.’ ”

On the flip side, she said, others are attracted to it because it looks like play.

“They want to fly,” Felinczak said.

“I’m really inflexible, so floor yoga never appealed to me,” said Kaya student Kelley Loder. With aerial yoga, “there are more fun, flippy things to do.”

Yoga inversions, such as handstands, are difficult to do on the floor; they take considerable strength. But in aerial classes, students eagerly flip upside-down and dangle from the silks.

“I cannot even explain to you how amazing that feels,” Kemp said about aerial inversions. “There’s much less weight on your wrists and shoulders, and it’s a true inversion.”

But while devotees rave about the spine-lengthening benefits of aerial yoga, they also admit that it is a tough workout.

Aerial yoga targets muscles other exercises do not, Felinczak said, such as the forearms and inner core muscles. Because of this, it can be just as challenging for seasoned athletes as for beginners.

“It’s a good equalizer,” she said, “because it develops muscles you wouldn’t be able to develop otherwise. You’re all starting from the same place.”

Both gyms have member and nonmember rates for the classes.

Kaya gets a lot of interest from devotees of strenuous CrossFit regimens, who often use the yoga to recover from an injury. The Philadelphia Eagles even came to one of Kaya’s classes. The studio also hosts corporate events, often used as a team-building exercise.

“It’s really hard to not laugh with people and get closer to them after doing something new and challenging,” Felinczak said.