Sentence:  It is made up of tumbling , which might be said to start with a somersault , run through such stunts as <WSD>headstands</WSD> , 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 a person balances on the head (usually with the help of the hands)