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In page Martial arts:

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In the seventies, lower ranks (kyu) began to be given colorful belts to show progress. This proved to be commercially viable and colored-belt systems were adopted in many martial arts degree mills (also known as McDojos and belt factories) as a means to generate additional cash. This was covered in the Penn & Teller: Bullshit! episode "Martial Arts" (June 2010).[citation needed]