Kids then move on to the intermediate/advanced tumbling class for ages 5 and up that teaches USA Gymnastics "compulsory skills." A ninjas class is also available for ages 4-7. Chelsea Piers ...

For many schools, the main activity of the day has long been kumitaiso, or group gymnastics. But critics argue that this traditional sport culture can be lethal. Kizo Hisamoto, the mayor of Kobe ...