Korean scientists think they have determined what caused a 39-story Seoul skyscraper to shake violently for 10 minutes, causing the building to be evacuated for two days.

Earthquake? Nope.

Gale-force winds? Sorry.

Volcanic activity? Unh-uh.

No, the culprit, they say, was 17-middle-aged gym rats working off the midriff bulge in a Tae Bo class.

Apparently, while dancing and boxing to “The Power” by Snap on July 5, the exercisers not only shook their booties, they shook the building.

“It just happens to be that the vibration set up by the Tae Bo exercises coincided with the resonance frequency unique to the building,” Chung Lan, professor of Architectural Engineering at Dankook University, told the Korea Times. “When an external vibration hits the resonance frequency of a certain object, the vibration is amplified and causes excess shaking even from slight movement.”

Six Architectural Institute of Korea professors and several vibration measurement experts inspected the building, a high-rise shopping mall, and carried out a simulation of the exercise class using the same number of participants. They agreed that mechanical resonance was the probable explanation.

Chung said the class had a new instructor who apparently worked the group twice as hard as usual.

Aerobic exercise blamed for tremor at Techno-Mart (Korea Times)

Gym rats shook TechnoMart: Owner (Korea JoongAng Daily)