London - England's Soccer World Cup squad have been training in sweat vests in Portugal as coach Roy Hodgson prepares them for the heat they will encounter in their opening match against Italy in the Brazilian city of Manaus.
Experts from Loughborough University are also monitoring players at the base in Vale Do Lobo.
"It's about learning to be comfortable being uncomfortable," Hodgson told the BBC.
"We tested how much they sweat, how they will be able to recover and what can be done to help."
England's opening match in the northern Amazon city of Manaus is causing particular concern as heat and humidity levels are likely to be intense.
Temperatures at Vale Do Lobo are mild in comparison but players are wearing several levels of clothing, while special pads monitor how much they are sweating.
When manager of Switzerland preparing for the 1994 World Cup finals in the United States, Hodgson used saunas to try and replicate the conditions his players would face.
"Compare that to what we are doing now and it was an unbelievably amateurish performance," Hodgson said.
After facing Italy, England play Uruguay in Sao Paulo, where temperatures are predicted to be far lower, while their last group matches is Costa Rica in Belo Horizonte, where heat and altitude could both be factors.