Gym Workout Caused Tremor at Seoul Building

South Korean experts said Tuesday a vigorous gym exercise session caused a high-rise building in Seoul to shake for 10 minutes earlier this month, prompting hundreds to flee it in panic.

In front of journalists they re-created the scenario on July 5 -- a group of 17 middle-aged people working out to the tune of a pop song, "The Power" by German group Snap -- and caused the building to shake in a similar way.

The group had been engaged in Tae Bo -- an aerobic exercise routine that combines boxing and martial arts like Taekwondo -- in the 12th floor gym of the 39-story TechnoMart mall building.

"Participants in Tuesday's test said they felt the building rolling greatly while others said they had felt lesser oscillations," TechnoMart spokesman Andy Yang told Agence France Presse.

Professor Chung Lan of Danguk University in Yongin city, who led the experiment, linked the incident to a physics principle governing the vibration of a structure when it is matched by another source.

He told a radio program the building, constructed from iron girders and cement, had a characteristic vibration frequency which was "in phase" with the synchronized movements of the Tae Bo practitioners,

After the first occasion the Gwangjin district government ordered the mall closed but reopened it after experts said it was structurally sound.

Cho Byung-Joon, an official with the district government, said earlier Tuesday that depending on the test results, officials might immediately allow the fitness club to reopen.

"But practicing Tae Bo in that particular building may have to be banned," Cho said.