The main muscle associated with hacky sack is the "Sartorius". It is the muscle that allows you to kick the hacky sack. You also use "psoas" and "iliacus," which are the muscles attach to the inside of the thighbone.
Footbag, more commonly known as Hacky Sack (a name trademarked by Wham-O!) is a sport that can be played individually or with a group of people by kicking a bag with your feet. In addition to the feet, pretty much any other part of the body can be used except for the hands or arms- just like in socce
Hacky Sack or Footbag, as we know it today, is a modern American sport invented in 1972, by John Stalberger and Mike Marshall of Oregon City, Oregon. Marshall had created a hand-made bean bag, that he was kicking around. Stalberger was recovering from knee surgery and was looking for a fun way to exercise his knees. Together, they called the new game "Hackin' the Sack." The two decided to collaborate and market their new game under the trademark of "Hacky Sack®".
Find out more facts about Hacky Sack and learn how to play it at Anoka-Hennepin School District - Hacky Sack Study Guide.
Check out some Tips for a Hacky Sack Beginner from HowTheyPlay.