Sentence:  It is made up of tumbling , which might be said to start with a <WSD>somersault</WSD> , run through such stunts as headstands , handstands , cartwheels , backbends , 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 feet roll over the head (either forward or backward) and return