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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.
More intensive versions of this jump include bending down (over) and touching the floor in between each jump.
A similar jump exercise is called half-jacks, which were created to prevent rotator cuff injuries, which have been linked to the repetitive movements of the exercise. They are like regular jumping jacks but the arms go halfway above the head instead of all the way above it. The arms also hit the sides to help tighten the jump.
Although he played no part in inventing the exercise, the late fitness expert Jack LaLanne was given credit for popularizing it in the United States. LaLanne used the jumping exercise during routines he promoted in decades of television fitness programming.
Ashrita Furman set the Guinness World Record for number of star jumps (jumping jacks) in one minute at 61, on May 17, 2008. In 2010, National Geographic Kids organized an event in 1050 locations as a part of Michelle Obama's "Let's Move!" exercise campaign in which 300,365 people were measured doing jumping jacks (for one minute) in a 24-hour period.