I lived in Japan for many years and every year we'd head out to Chiba where there's a sports university and we'd participate in a cultural exchange of sorts. Basically for 5000 yen which was about $50, we'd dorm there for three days and participate in certain martial activities. It was open to all foreigners in Japan who did martial arts and were at least shodan or black belt. Each time it was more or less the same thing. The first night there was the introductory kampai followed by introductions, dinner and lots of drinking and carrying on. The next morning, after breakfast, was the introductions to all the different events going on. Sometimes we'd head out, in our gear, to one of the campuses where there was a demonstration and we'd participate. Other times we'd hit the gym and practice our style. Then there were the opportunities to try other styles, one of which was sumo.
Say what you want about sumo being fat, these guys are fit like motherfuckers. Flexible, strong and on the younger ones you could see the muscles especially in the shoulders. These guys were built. During the introduction to sumo, they mentioned that no they don't suck their balls into their body even though Westerners think they do. There was much laughter at that and embarrassingly we sucked at trying to push one of these guys out of the ring, even two of us at a time.