from Tongan at the end of 2006, allowing another Tongan to enter his stable, and Kyokutenhō's change of citizenship allowed Ōshima stable to recruit Mongolian Kyokushūhō in May 2007. However, on February 23, 2010 the Sumo Association announced that it had changed its definition of "foreign" to "foreign-born" (), meaning that even naturalized Japanese citizens will be considered foreigners if they were born outside of Japan. The restriction on one foreign wrestler per stable was also reconfirmed. As Japanese law does not recognize subcategories of Japanese citizen, this unique treatment of naturalized citizens may well be illegal under Japanese law, although the restriction has never been challenged in court. in contrast to other martial arts practitioners While sumo is considered a martial art, it diverges significantly from many other typical Eastern martial art styles, in both presentation and structure. Whereas most martial arts award promotions to practitioners through time and practice, a 's sumo rank can be gained and lost every two months in the official tournaments. Conversely, in more common Japanese martial arts (such as karate), ranks are gained after passing a single test, and practitioners of karate are not normally demoted, even after repeated poor performances at tournaments. This divergence from other martial arts creates a high-pressure, high-intensity environment for . All the benefits that wrestlers receive can be taken from them if they fail to maintain a high level of achievement in each official tournament (or ). Furthermore, sumo does not provide any means of achievement besides the official tournaments. A 's rank is determined solely by his number of wins during an official tournament. On the other hand, in many other Eastern martial arts, competitors can display their skill by performing standard routines, called or forms, to receive recognition. Thus, sumo wrestlers are very specialized fighters who train to win their bouts using good technique, as this is their only means of gaining better privileges in their stables and higher salaries. Former in mixed martial arts The numerous differences between sumo and its martial arts counterparts have not deterred many former sumo wrestlers from competing in mixed martial arts. Most have had limited achievement; perhaps the most successful sumo wrestler to have competed in MMA is Tadao Yasuda, who holds a record of two wins and four losses. Sumo wrestlers are seen as generally ineffective in MMA because the sports are vastly different from one another