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 %.
