(NBC) - In a San Francisco studio, there are no looky-loos. Everyone here has joined the inner circle.
At the center of this spinning mayhem, is former anthropology major turned hooping guru, Christabel Zamor.
"When I was studying to be an anthropology professor, I had a very conservative views of how I could become successful in the world and hooping sort of took my life by storm," Zamor said.
Nine years ago, Zamor stepped into what was then an underground hooping resurgence.
Since then her company Hoop Girl has trained thousands to spin, whirl and hoopdance.
Anyone who thinks that hooping is a child's pastime hasn't taken one of Zamor's classes.
It's an intense workout that isn't for the faint.
"Yes, oh my gosh, especially in your abs, I really can feel it. It's a great strength builder. Legs, absolutely," Kitty Gordon said.
Over the past few years, hooping has exploded across the US.
Even first lady Michelle Obama has stepped into the ring.
"Hoopdance definitely delivers a high body workout. It's not just strength building but also cardiovascular, builds endurance, core strength," Zamor said.
Zamor says hoopers in her class can burn 600 calories an hour.
But for many, the draw is the plastic ring's spiritual side.
"It's a calming feeling for me. I enjoy that part of it. It's like it get to settle down once I get in the hoop and just dance and be whoever I be," Lisa Rizzoli said.
While the hoop is enjoying a second life, don't consider it a passing fad.
This time around, it's putting a whole new spin on exercise.