Osaka: The Wallabies are adjusting their training routines after arriving in Japan as the country suffers through the third week of an oppressive heatwave, which got so extreme last week it was officially recorded as “cruelly hot” for the first time in the nation’s history.

The term “kokushobi” – which translates as “cruelly hot day” – was introduced by the Japan Meteorological Agency in April after an online public vote to name a day that gets above 40 degrees. There is already a term for more than 35 degrees – moshobi or “extremely hot day” – and those have been almost constant during the past three weeks throughout Japan.

In Osaka, sardine-tin subway carriages are crammed with of hot-and-bothered locals, many of whom have taken to carrying small battery-operated fans.

The Wallabies joined in the locals’ suffering as they sweated through their first training session in Osaka on Monday before their clash with Japan on Saturday.

The temperature in Osaka reached 37 degrees, which is even getting a touch hot for Aussies. The forecast highs for the rest of the week are similarly toasty, and even night temperatures are in the high 20s.

But unlike Australia’s dry heat, Japan’s conditions get even more oppressive with the extreme humidity factored in.

The humidity in Osaka on Monday was 68 per cent, which had some weather websites calculating the “feels like” temperature at closer to 45 degrees.

For the big Wallabies forwards with an average weight of 117kg, it would have felt “cruelly hot″, even at a lighter training session.

The side is set to have a more intense day on Tuesday and team officials have adapted training times and will allow for more water breaks, and use cooling methods to lower body temperatures between sessions.

A bit like the issue of jet lag when playing in South Africa, the Wallabies aren’t keen to make a big deal of the heat, particularly given Japan’s players are used to the tropical conditions.

“Obviously it’s pretty warm over here, but I grew up in Brissie,” Wallabies hooker Josh Nasser said.

“The humidity is up, the temperature is up, but it’s no different to some of the conditions we get back home.”

New Wallabies defence coach Scott McLeod, who has played and coached in Japan, said the team had done lots of work in the past week in Sydney with the expectation they would need shorter sessions in the heat this week.

“That’s enabled us to be smart around the time we’re on our feet this week,” he said. “We still need the boys to feel that intensity and what it feels like, and we’ll definitely do that tomorrow and Thursday. But we’re able to manage that well because of the work we’ve already put in.”

Asked if Japan have an advantage in the conditions, McLeod said: “No, I don’t think so. They live in it day to day, so they know how to manage that and how to feel that, and it doesn’t really come into their psyche about it, whereas visitors here will go, ‘Oh’, and they will just keep referring to it ...

“But these guys will just get on with the job, and that’s the space we need to live in as well.”

There is no getting away from the heat, however. The extreme temperatures, caused by a high-pressure system covering large parts of Japan, are forecast to last until at least Sunday.

The conditions could theoretically threaten the Test match on Saturday night, given they may push the limits of World Rugby’s heat guidelines.

Under a revised policy introduced last year, a “heat stress index” calculation is made based on air temperature, humidity, wind speed and the level of thermal radiation in the environment.

Generally speaking, less than 30 degrees and 60 per cent humidity is considered acceptable, and will give an index of less than 100. But if the HSI is between 100 and 250, increased cooling measures are mandated, such as more water breaks and a longer half-time.

If the heat index is extreme, at 250 or more, the game can be delayed or even suspended.

However, the game doesn’t appear to be in danger. Long-range forecasts show the temperature in Osaka will fall to 28 degrees on Saturday night, and rain is also forecast.

Nasser said the conditions could get slippery, but that would not stop the Wallabies looking to play an expansive game.

“A bit like in the wet, the ball gets slippery and things tighten up a little bit,” he said.

“But I think we’ve got a big focus on still trying to express ourselves. We play a fixture in Fiji each year where we get pretty extreme conditions.

“Obviously, fatigue will be a factor, but that’s the same for both teams. It’s not something we’re really hyper-focused on – just accept that it will be hot, and then sticking to our processes.”