Novak Djokovic may be one of the fittest athletes in the world but the world number one wrestled with rare feelings of being hopelessly out of shape during a workout with retired sumo professionals on Monday.
The 32-year-old Serb, who is in Tokyo to play in the Japan Open Tennis Championships, visited a traditional dohyo or a sumo ring to watch the wrestlers during their morning practice before unsuccessfully attempting to make one of them budge.
"I felt I'm out of shape (for sumo) a little bit ... with a few more kilos, I'll be ready to compete. Probably three times as much as I have right now would be the right measurement for me to compete," Djokovic told the ATP website.
"It's quite impressive to see also how flexible they are ... I didn't think that they were that flexible considering it's a heavyweight sport.
"But I see that they are paying a lot of attention to the mobility of their joints ... which is of course what allows them to move around as agile as possible at their weight."
Djokovic, who plays Australian Alexei Popyrin in the first round on Tuesday, recalled watching yokozuna Akebono who became sumo's first foreign-born grand champion in 1993.
"It's a great experience ... one of the most popular sports in Japan. Speaking with my father yesterday on the phone I was telling him that I'm going to have an opportunity to meet sumo wrestlers," 16-times Grand Slam singles champion Djokovic added.
"He and I were remembering many years ago when we used to watch Akebono ... someone we supported a lot."