JJ meaning in Sports ?

A jumping jack, also known as a star jump and called a 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 going overhead, sometimes in a clap, and then returning to a position with the feet together and the arms at the sides.

The name origin for the jumping jack exercise has sometimes erroneously been identified as World War I U.S. General John J. "Black Jack" Pershing, who is said to have developed the exercise, but in fact the name comes from the jumping jack children's toy, which makes similar arm swing and leg splay motions when the strings are tugged.

Although he played no part in inventions 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.