The aim of this study was to clarify the effects of the expansion of the dohyo (the ring in which sumo bouts are performed) on the winning percentage for a lighter wrestler, the number of kimarite (the winning techniques in a sumo bout) and the competitive time. Forty-four pairs of collegiate sumo wrestlers, 21 pairs with a large weight difference (above 10 %) and 23 pairs with a small weight difference (below 10 %), performed 10 bouts of sumo in both a standard dohyo (diameter: 4.55 m) and an expanded dohyo (diameter: 4.85 m). We evaluated the winning number for a lighter wrestler, the number of kimarite and the competitive time in the 10 bouts.
The following results were obtained.
1) The winning number for a lighter wrestler was 4.67 ± 1.35 (average ± SD) bouts in the standard dohyo and 5.52 ± 1.33 bouts in the expanded dohyo (significant difference, P < 0.01) among the pairs with a large weight difference. On the other hand, the winning number was 4.91 ± 1.70 bouts in the standard dohyo and 5.30 ± 1.72 bouts in the expanded dohyo (NS: no significant difference) among the pairs with a small weight difference.
2) The number of kimarite was 4.90 ± 1.14 te in the standard dohyo and 4.95 ± 1.28 te in the expanded dohyo (NS) among the pairs with a large weight difference. The number was 4.00 ± 1.04 te in the standard dohyo and 4.61 ± 1.56 te in the expanded dohyo (NS) among the pairs with a small weight difference.
3) The competitive time was 8.67 ± 3.95 s in the standard dohyo and 8.80 ± 3.09 s in the expanded dohyo (NS) among the pairs with a large weight difference. The time was 8.47 ± 3.28 s in the standard dohyo and 8.92 ± 3.06 s in the expanded dohyo (NS) among the pairs with a small weight difference.
These results suggest that the expansion of the dohyo (from 4.55 m to 4.85 m of the diameter) increases the winning percentage for a lighter wrestler when the weight difference of a pair is above 10 %, but there is little affect when the weight difference of a pair is below 10 %.

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本発表は70年代に現役時代を送った元力士の聞き取りをもとに、2つの視点から発表を行う。まずは当時の、番付による序列、入門時期による序列が色濃く反映された大部屋の部屋の様子を明らかにすることで、当時の社会、文化がどうであったかを読み解く。次に、元力士の引退後の活動に着目し、各界から去った彼らがどのように部屋と関わり、文化を築き上げているのかに関しての考察を行う。

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  The Nihon Sumo Kyokai has been making local tours in addition to holding its regular tournaments. Until 2001, the tours were sponsored by companies and operated by the Kyokai itself. In 2002, the Kyokai lost the sponsors and it became difficult to maintain the business model of the tour. So, from 2003, the Kyokai decided to change the business model and began to sell each event of the tour to local promoters.
  In this paper the background and purposes of the change of the business model are examined, and the influence of this change is considered.
  As the result of the change, the Kyokai became free from the financial risk of the tour. But at the same time, the number of events of the tour decreased because the number of local promoters who had ability to take the financial risk of the event was not enough.
  The Kyokai has a philosophy of trying to popularize sumo, and local tours are one of the means to attain it. But it seems there is a trade-off between this philosophy and financial risk of local tours. If the Kyokai wants to hedge the risk, the number of events of the local tours will decrease, so the Kyokai will not be able to attain the philosophy. If the Kyokai has a strong will to attain the philosophy and to hold more events, its financial risk will become larger.

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平成元年1月から31年4月に当院を受診した大

力士1,590例5,268件を対象に，部位別頻度とその内訳について調査した．体幹傷害1,325件（25.2％）の部位内訳は，頸椎355件（6.7％），胸椎・胸郭141件（2.7％），腰椎722件（13.7％）であった．上肢傷害1,115件（21.2％）の部位内訳は，肩関節323件（6.1％），肩鎖関節141件（2.7％），肘関節248件（4.7％），手・手関節326件（6.2％）であった．下肢傷害2,771件（52.6％）の内訳は，膝関節1,489件（28.3％），足関節427件（8.1％），足387件（7.3％）であった．全体の過半数を占める下肢傷害ではLM損傷やACL損傷が多く，ACL損傷223件のうち130膝に対して鏡視下ACL再建術を施行した．

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The purpose of this study was to examine the specificity of power at “Tachiai” in Sumo wrestlers and the relationship between its power and force in “Atari (impact)”.
Two kinds of power from the “Shikiri” position and standing start position were measured by the method of inertia wheel loading. The loads (equivalent masses) were 35.2kg,53.3kg,89.9kg,182.9kg, and 556.7kg.
The force in “Atari” was measured as the maximum impulsive pressure against the vertical force plate. Subjects were five top and five intermediate-level intercollegiate Sumo wrestlers.
The following results were obtained:
1) From both the “Shikiri” position and the standing start position, the top-level wrestlers generated greater power than the intermediate-level. Two differences were significant (p<0.01). The difference regarding the “Shikiri” position was particularly remarkable.
2) With the intermediate-level wrestlers, power from the “Shikiri” position was remarkably less than from the standing start position. Its difference was statistically significant (p<0.01).
3) Concerning the top-level wrestlers, there was no significant difference between power from the “Shikiri” position and that from the standing start position. Power at the top-level obtained from the “Shikiri” position was less than that from the standing start position at loads of 35.2kg,53.3kg, and 89.9kg. However; the “Shikiri” position with heavier loads of 182.9kg, and 556.7kg, showed signs of producing equal or greater power than the standing start position.
4) The mean of the maximum impulsive pressure among the top-level wrestlers was greater than that among the intermediate-level by about 25%, though its difference was statistically nonsignificant.
5) All coefficients of correlation of power from the “Shikiri” position to maximum impulsive pressure and to body weight were significant except for that with the lowest load. As the load got heavier, the coefficient became greater (Table 5). In addition, the correlation coefficent of maximum impulsive pressure and body weight was significant (r=0.711, p<0.05). The partial correlation of power from the “Shikiri” position and maximum impulsive pressure, excluding the factor of body weight, ranged nonsignificantly from 0.285 to 0.478.
These results suggested that the “Shikiri” position might be a very disadvantageous position for the intermediate-level wrestlers in trying to produce greater power.
Moreover, body weight was found to play an important role in generating power from “Shikiri” and force in “Atari”.

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This study focuses on sumo in the middle ages of its history, namely samurai sumo, and re-examines sumo in this period from the perspective of samurai as entertainers during that time.

Today Japanese people consider samurais as noble and loyal warriors. This image has been conceptualized and established in the minds of the people through the nationalistic education of Japan since the Meiji period. However, the primordial question that arises from the freedom of thought and learning, which allows one to greatly diverge from the retrospective image of samurai warriors thus far, has led to the common belief that samurais were also once entertainers.

Based on this theory, sumo in the middle ages can then be regarded as samurai sumo, which can be considered as entertainment. This can be attributed to the fact that since the mid-Heian period, sumo has been refined into a form of entertainment as a spectator sport, the primary purpose of which was to inspire and entertain the emperor and aristocrats of that time. During the late Heian period, in the provincial governing system that organized Japan into a single state, sumo was divided among specific houses and passed on through generations as a family business.

Kyosumo, also known as Kyoto Sumo, is an organization to which professional sumo wrestlers belonged. These sumo wrestlers, whose ancestors performed at the ancient Japanese imperial court, would perform at festivals in major temples and shrines in and around Kyoto during the end of the Heian period. This form of “sumo for entertainment” that had been refined into a spectator sport also existed during the middle ages of Japan around the Shogunate. Originally, the samurai leaders also viewed sumo as a spectator sport that was performed by special sumo wrestlers for the entertainment and pleasure of the audience.

In this sense, when we consider sumo in the middle ages from the perspective of samurai as entertainers, closely analysing samurai sumo, we can conclude that sumo was also a form of entertainment.

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[Purpose]] We examined student sumo wrestlers in order to study the relationship between their sports performance and the muscle strength around their shoulders.
[Materials and Methods] Twenty-three wrestlers were examined in 2000. Twelve were collegiate and eleven were high school wrestlers. The isokinetic strength of their internal (IR) and external (ER) rotators and flexor (FX) and extensor (EX) were measured using a Cybex. We also divided them into two groups : strong group and weak group. Strong group has higher sports performance than weak group in sumo wrestling.
[Results] Their mean height was 177.6cm, weight 108.6kg, body mass index 34.3kg/m². Their IR, ER, EX and FX of strong group was significantly larger than one of weak group, but the ratio of strength to their weight, the ratio of ER to IR and the ratio of FX to EX between strong group and weak group had no significant difference.
[Conclusion] In order to improve their sports performance of student sumo wrestlers, it was significant to increase their IR, ER, FX and EX, especially.

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We examined high school sumo wrestlers in order to study the relationship between their sport performance and the muscle strength around their shoulders.
Materials and methods: Sixteen wrestlers were examined in 1998. The isometric strength of their internal and external rotators were measured using a Micro-FET(M), and the isokinetic strength of their internal (IR) and external rotators (ER) and flexor (FX) and extensor (EX) were measured using a Cybex(C). We also divided them into two groups; strong group (S) and weak group (W). Results: Their mean height was 175.9 cm, weight 99.5 kg, body mass index 32.1 kg/m2. In C, their FX and IR of S was significantly larger than those of W, but the ratio of EX and ER to their weight between S and W had no significant difference. IR increased more than EX for about 6 months. Conclusion: To improve their sport performance in high school sumo wrestlers, it was significant to increase their FX and IR, especially.

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Sumo dates back approximately 350 years to the Edo period. The sport is rich in history and tradition, and has always played an influential role in Japanese society. However, in recent years, the number of violent incidents involving sumo athletes outside of the ring has been increasing. These incidents have placed a spotlight on the Japan Sumo Association and led to a higher demand for more rigorous risk management approaches. This study aims to evaluate the effectiveness and practical application of current risk management for preventing cases of violent assault in sumo and to elucidate the steps being taken by the Japan Sumo Association to achieve this.

Past violent incidents were investigated to evaluate the effectiveness of current risk management approaches and analyze how these approaches have been applied as a countermeasure. To evaluate the effectiveness of current risk management approaches, all risk events were extracted from both external and internal sources, using the Risk Breakdown Structure, a tool for structuring the risk process. Two main external events are sumo’s traditional customary system and the living environment of sumo athletes. Internal events include the sumo athletes’ physicality, personalities, and mind-set. The validity of these events was reviewed by conducting interviews. The practical application of current risk management approaches was analyzed using self-evaluations and questionnaires.

The results revealed no significant problems in the practicality of current risk management approaches; however, defects were found in the application of countermeasures. These findings suggest that the Japan Sumo Association needs to review its current risk management approaches to reduce the number of violent incidents involving sumo athletes and implement more effective measures.

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The purpose of this study was to investigate the relationship of competitive ability to body weight, body composition, isokinetic strength, and maximum anaerobic power in college Sumo wrestlers. We divided the subjects into a regular group (RG: n = 5) and a substitute group (SG : n = 6) on the basis of their competitive ability. In the RG, we valued the competitive ability by their winning rate of competitions. We measured the above parameters three times (before the season: pre-season, in season: inseason, and after the season : post-season) in a season. Then we analyzed the relationship of competitive ability to the change of the parameters during the season.

1) Body weight and fat weight (by air displacement method) of RG was significantly higher (p < 0.05) than SG at in-season and post-season. % Fat of RG was significantly higher (p < 0.05) than SG at post-season. In the RG, subjects who gained body weight (by fat or LBM) increased their winning rate during the season.

2) All of measured isokinetic strength (Cybex 6000) of the RG was higher than SG. Knee flexion, elbow extension and flexion were significantly higher (p<0.01 or p<0.05) than SG at 180 and 300 degree/sec-1 in post-season. In the RG, subjects who gained the strength at 180 and 300 degree/sec-1 increased their winning rate.

3) Maximum aerobic power (by cycle ergometer dynamometer) of the RG was higher than SG but there was no significant difference between the groups. In RG, the intergroup of maximum anaerobic power significantly increased (p < 0.01 or p < 0.05) during the season.

These results suggest that gain in body weight (either fat or LBM) is important to increase the competitive ability. Moreover, Sumo wrestlers need plyometrics and ballistic training that increase physical function in order to perform with high power in short time during the season.

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