England are planning hot weather camps in Italy next summer to prepare for the conditions expected at the 2019 World Cup, knowing that some players will battle in the Japanese heat.
Eddie Jones will take his squad to Treviso for two eight to 10-day spells in July and August ahead of their tournament opener against Tonga on September 22.
In the build-up to their June tour to South Africa, England turned their indoor training centre at their Bagshot base into a sweat box designed to mirror the humidity and temperature of Japan.
It was during that experiment that certain players were exposed while others - such as Owen Farrell and George Ford - showed no adverse effects.
"The common sense approach is that if you're playing in warm weather, get used to it physically, mentally and skill wise," Jones said.
"Treviso's climatic conditions are very similar to the possible conditions we could encounter in Japan and climatic synergy is good.
"I don't see Treviso as identical but it's useful in being able to trial things before the World Cup. We're trying to dress rehearse it.
"Some players definitely perform better than others. We've already heat tested the players once and there were a number of them who have a negative reaction.
"You do all their blood and saliva testing to find out how they're coping. We have to do more work in getting them right to cope with heat.
"The usual players did well such as Farrell and Ford. The good players always find a way to react.
"Others struggle to retain their work rate and then struggle to retain intensity in terms of skill execution. They're the two factors."
Asia's first World Cup will be staged during a period of the year when Japan is subject to catastrophic weather events, resulting in extensive contingency planning by tournament organisers and competing teams.
"You could have three days where you can't train outside so we're definitely coming up with plans to train inside," Jones said.
"But if there's a typhoon on you can't use the roads so you can't leave your hotel."
