Watching two sumo wrestlers in a practice bout is a surprisingly quiet affair.

A Japanese phrase is issued to kickstart the match before some dull slaps of skin against skin.

Training in a small reserve in Mosman in Sydney's north on a chilly August day are Jack Carlson and John Trail.

Carlson isn't your stereotypical sumo wrestler.

He's only 78 kilograms, in his first year of a medical degree and has very little "puppy fat".

"The diet is pretty important but I can pretty much eat what I like," the 18-year-old said.

"I'd like to go up to 85 kilograms and put on as much weight as I can."

Jack hits the gym and tries to eat four to five protein-heavy meals per day. ( ABC Radio Sydney: Amanda Hoh )

Carlson has been sumo wrestling since he was young, and was the Oceanic junior champion in 2015 in his first year of competing professionally.

The sport runs in the family.

Carlson's cousin is also a wrestler, and Trail, the family's trainer and Carlson's uncle, is president of the Australian Sumo Federation.

"It's steeped in tradition, a very ritualistic sport, very primal," Carlson said.

"It's also very simple — easy to learn, hard to master."

Not all about the kilos

Sumo is still a fairly niche sport in Australia and has a small community that regularly compete against each other.

There are three categories — lightweight for those under 85kg, middleweight (85-115kg) and heavyweight (115kg and over).

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Compared to international athletes, particularly in Japan where the sport is revered and respected, the wrestlers in Australia tend to want to lose weight rather than gain it.

"You might think sumo wrestling is all about putting on the kilos, but for the Australian team it's often about losing the weight to drop down a category," Trail said.

Diet is of course a key component of the training regime.

"With the eating, it's a bit of a myth it's about being fat," Trail said.

"[The Japanese] eat a very healthy diet called chanko — it's a hot pot with low calories and they go to bed with a full stomach.

"It gives you the puppy fat to protect your organs from the impact."

Endurance over weight

Strength, discipline and flexibility are important skills for a sumo wrestler.

With the raw combat style, being heavy-set doesn't necessarily guarantee a win.

For Carlson, improving his endurance will hopefully give him the upper hand.

"Sumo wrestling is a lot of strength and speed ... so if I can withstand the initial barrage I can wear out my opponent," he said.

John and Jack usually train in the Pearl Bay reserve in Mosman. ( ABC Radio Sydney: Amanda Hoh )

Carlson will be competing in the Sakura Cup at the Cherry Blossom Festival in Auburn on Sunday.

Sumo wrestlers will be coming from as far afield as Fiji, Mongolia, Vietnam and Tonga.

And while the main rivals and most intimidating will be the Tongans, Carlson said most sumo wrestlers were "kind enough not to hurt you".

"The scariest guys are usually the middleweights, so that's when you need to be concerned how hard they will hit you," he said.

"But if they're giant they usually try and put you safely to the side."

Tune in to ABC Radio Sydney live from the festival from 10:00am on Sunday, August 26.