U.S. patent #4565370 was granted on January 21, 1986 to Tony Christianson for a “foot holding device for hanging upside down.” Mr. Christianson’s patent makes pointed reference to earlier, roughly similar inventions—especially to one by R.M. Martin, who was granted U.S. patent number 3,380,447 on April 30, 1968 for an “ankle device for supporting an […]