Eight students in Osaka Prefecture suffered broken bones during a three-year period at a public junior high school while practicing or performing kumitaiso, the gymnastic formation known as a human pyramid.

Kumitaiso is a popular and long-running feature of sports events at Japanese schools, but the practice has also been the cause of serious injuries, raising safety concerns.

At Taisho Junior High School in Yao, Osaka Prefecture, a 10-tier human pyramid — where students kneel in rows on each other's backs, with the top person standing — collapsed during a performance on the school's sports day on Sept. 27.