jumping jacks

John GrishamのPlaying for Pizzaを読んでいます。
He was Alex Olivetto, a former player, now an assistant coach, and a real Italian. He strutted up and down the lines of players barking orders like an angry field marshal, and there was no back talk. “He's psycho,” Sly said when Alex was far away. Rick was at the end of a line, next to Sly and behind Trey, copying the stretches and exercises of his teammates. Alex went from the basics--jumping jacks, push- ups, sit-ups, lunges--to a grueling session of running in place with an occasional drop to the ground, then back up.
"jumping jacks" はローリングストーンズの "Jumping Jack Flash" を連想させますが、ジャンプをする運動に違いありません。実際にはどんな動きでしょうか？
・Oxford English Dictionary: A calisthenic jump done from a standing position with legs together and arms at the sides to a position with the legs apart and the arms over the head.
この様な場合は辞書よりも百科辞典の方が詳しいはずなのでWikipediaを見ると次の説明がありました。
A jumping jack (Canada & US) or star jump (UK and other Commonwealth nations), also called side-straddle hop in the US military, is a physical jumping exercise performed by jumping to a position with the legs spread wide and the hands touching overhead, sometimes in a clap, and then returning to a position with the feet together and the arms at the sides. The jumping jack name comes from the traditional toy of the same name, while "star jump" refers to the person's appearance with legs and arms spread.
The jumping jack is the official state exercise of Missouri, USA as of July 2014.
動きがある場合には百科辞典よりも現代はYoutubeですね。Youtubeには "jumping jacks" の実演が幾つもあります。