Wikipedia
A joggling or jostling board is a long, pliable board that is supported on each end by wooden stands. The board is springy and a person sitting on it can easily bounce up and down. Sources differ on the origination; its usage in the Lowcountry of South Carolina around Charleston in the early 19th century is however rather well-documented.
Traditionally, it is painted Charleston green. The joggling board's popularity has slowly been coming back, mostly as decorations on lawns and front porches.
Martha Graham bought several joggling boards from Old Charleston Joggling Board Co. 1 on a visit to Charleston and used them as props in her dance Maple Leaf Rag. Photos from the rehearsals show the variety of ways the board was used. The company posed with Graham on these boards for the New York Times.