Parkour co-founder Chau Belle trains in a park in Paris, Thursday, Dec. 20, 2018. Belle was one of nine co-founders of the street sport born in the suburbs of Paris in the 1990s. Parkour is involved ...

Parkour — once synonymous with an outlaw, fence-hopping subculture — became one of the fastest-growing fitness trends in the U.S. last year, according to ClassPass. Why it matters: The sport all about ...