Jumping jacks are great as you can stop and do jumping jacks anywhere. Just be careful of who is around you as you don’t want to whack anyone. Follow these links to see some advice on how to perform a jumping jack and some reasons to include them in your HiiT workout.
http://www.wikihow.com/Perform-Jumping-Jacks
http://www.bodybuilding.com/exercises/detail/view/name/jumping-jacks
http://sacdt.com/dt/blog/2013/06/variations-of-jumping-jacks/