The lights were dimmed. The music was blaring. The dance floor was bustling.

But this wasn't the standard disco scene.

All of the dancers were female. Instead of heels and skirts, they wore sweats and sneakers. With no bar in sight, the ladies sipped water.

This is "Dance Dance Party Party," a throwback to the sweaty days in the middle-school gym, the bouncing hours in the family basement, the no-holds-barred-fun that was possible before puberty and self-consciousness took over.

Each week in a South Philadelphia dance studio, women take part in the unstructured exercise class - really a 90-minute dance free-for-all. It was originally conceived in New York in 2006, and Graduate Hospital roommates Michiko Hunt, 32, and Rachel Myers, 29, brought the concept to Philly in January.

"We basically did this because we like to dance," Hunt said. "We all remember being 12 and having slumber parties. It's a little bit of that, too."

The biggest "rule," if you can call it that, is "No judgment." You don't do it to others; others don't do it to you. If you want to do the Monkey across the room, no one says a word. If you want to break into a choreographed routine, your moves are appreciated but unremarked upon.

"It's really fun seeing other people have fun. This is all about feeling free and not caring what anybody thinks," Myers said.

Out at clubs and other judgmental places, "the people standing on the sidelines scowling are just envious," Hunt said.

Although they take some weeks off, Hunt and Myers host events Sunday afternoons at Arts Parlor, a rented studio space on South Broad Street near Ellsworth. Although there's a $5 cover charge, this isn't a moneymaking venture. The size of the crowd varies each week - "Sometimes it's me and Rachel and one other girl," Hunt said - and the money goes toward studio rental space, monthly dues to be part of the DDPP network, and paying off the Bose sound system Hunt purchased for the events.

On a recent Sunday, 10 women joined Hunt and Myers at the dance studio. The first thing they did was pull gray curtains over the mirrors and dim the lights. Most of the participants were in their 20s and 30s, but all ages are welcome. All sizes, too: Hunt said one past participant found the group via a fat-acceptance blog.

Only men are excluded. Some, like Myers' brother, have complained they feel left out of the fun. "He always jokes he's going to cross dress and come to DDPP," Myers said.

An absence of males means the women can do their craziest or sexiest dance moves without fear of censure or inadvertently sending the wrong signals. Victoria Pendragon of Riverside described her dance style as "fetching" and said that was one reason she enjoyed the events.

"At 62, I don't need that attention," she said.

A former go-go dancer - with high boots and short skirts, she said - Pendragon discovered DDPP when she was living in Rhode Island and, for six months running, she never missed a weekly event. When she recently moved to New Jersey, she immediately looked for a local group.

"I couldn't live without it," said Pendragon. "You know you always want to dance and you don't always want a partner."

Mona Pandeya, 27, said she felt the same way. She and her two DDPP-attending pals - Ali Brunger, 29, and Anita Prabhakaran, 33 - had gone dancing over the weekend and Pandeya ended up running around a table to lose an unwanted suitor.

"I don't have to deal with that here," she said.

The three friends also liked that they weren't crowded on the dance floor and that although the music was loud enough, they could still talk and laugh with one another. They've come to about five Sunday gatherings.

"This weekend, every time we were dancing, we were like, 'It's not like DDPP,' " Prabhakaran said.

When the music started, a few people began to stretch while some continued talking.

"The first five minutes each week, I'm like, 'This is really awkward,' " Hunt admitted. "But once you get going, it's great fun."

Then one woman clasped her hands together and began swinging them over her head, an attempt to loosen up and to get things going. By the second song, Eurythmics' "Sweet Dreams (Are Made of This)," everyone was moving.

The songs kept coming - Prince, Madonna, Erasure. Pandeya and her friends laughed as they tried fancy foot moves, and Pendragon, in a world all her own, moved in and out through the crowd of dancers. Sometimes the women clapped after a particularly fun song, like "You're the One That I Want" from Grease, but, in general, there was little talking between songs - just the sounds of people catching their breath.

Lisa Vaccarelli, 29, a DDPP veteran, said some of her friends didn't understand how she could dance for an hour with strangers. She likes it because people move from being lost in their own thoughts to dancing with the group to wandering off again. She wouldn't miss a session.

"Sometimes I have to drag myself here because it's Sunday night, but I'm always in a great mood when I leave," Vaccarelli said. "It's a great way to end the weekend."

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