Sentence:  It is made up of tumbling , which might be said to start with a somersault , run through such stunts as headstands , handstands , cartwheels , <WSD>backbends</WSD> , and culminate in nearly impossible combinations of aerial flips and twists and apparatus work . 
Meaning of the word marked with <WSD> tags:  an acrobatic feat in which the trunk is bent backward from a standing position until the hands touch the floor