LONDON, July 23 (Xinhua) -- Following are the 10 useful facts about judo. The judo competition at London 2012 Olympic Games take place at ExCel from July 28-August 3:
1. Judo is a traditional Japanese martial art that developed from the various martial arts used in Japan over hundreds of years, mainly jiujitsu. The name consists of two Japanese characters, 'ju' (gentle) and 'do' (way, path). The base of modern judo was developed by Dr. Jigoro Kano in 1882.
2. Men's judo was introduced as an Olympic sport at Tokyo 1964. It was the first, and for a long time the only, martial arts discipline at the Olympic Games. Women's judo became an Olympic sport at Barcelona 1992.
3. The International Judo Federation has 200 members, and 134 have entered athletes for the London 2012 Olympic judo event. This ranks judo among the top five events in terms of the number of competing NOCs at London 2012.
4. The competition area is divided into two zones: the contest area (8x8m) on which the judoka compete, and the safety area (at least 3m wide). The two zones are distinguished by different colors.
5. One referee and two judges supervise the contest.
6. Contestants wear a blue or a white judogi.
7. Judo consists of seven weight categories. The categories for men are -60kg, -66kg, -73kg, -81kg, -90kg, -100kg and +100kg. The categories for women are -48kg, -52kg, -57kg, -63kg, -70kg, -78kg and +78kg.
8. A judo contest lasts five minutes. In the case of a tie, an extra round of three minutes is added, in which the first score, the 'golden score' decides the bout. If no competitor scores, the refereeing officials decide the winner by judging their superiority (known as hantei).
9. Competitors score points for actions such as throws and holds: yuko (the smallest point), waza-ari (half point) and ippon (full point). There are three ways to gain ippon, and each way forces the end of the bout. Ippon is awarded for a powerful throw, or for holding the immobilized opponent for 25 seconds, or if the opponent gives up ('taps out'), usually while in an armlock or choke hold. Two waza-ari add up to ippon (waza-ari-awasete ippon), but numerous yuko do not add up to another points value.
10. A penalty, known as shido, can be given by refereeing officials. Shido is mostly given for inactivity or evasion. The first shido is 'free'. Two shido add up to a yuko for the opponent. Three shido are a waza-ari for the opponent. Four shido lead to disqualification (known as hansoku make).