England have been training so hard that some players have been losing two kilograms per session, according to Ben Foster.
England have come to Miami to experience the same hot and humid conditions they will encounter in Manaus, where they play Italy on June 14.
Even in the cooler climes of Portugal and Burton-upon-Trent, the England management have tried to recreate Amazonian conditions by making the players wear several layers so they sweat more.
And Foster has also revealed that the players have been put through “brutal” sessions on exercise bikes in saunas to improve their fitness.
“When we were in Portugal we wore underarmour, t-shirts, zip up tops and a wet top over that,” the England goalkeeper said.
“When it was 22 degrees (centigrade) the lads were losing 2kg in sweat in every training session.
“We are trying to replicate the heat and humidity (of Brazil)
“Even at St George’s Park last week we trained in the morning, lunch, slept for an hour and then did bike sessions in heat chambers to get ready.
“We’ve been doing half hour sessions in there. It’s brutal, really hard work. But no-one’s grumbled or moaned about it, just got on with it.”
Roy Hodgson has left no stone unturned in his bid to get the players in the best possible condition for the World Cup.
The England boss has brought a psychiatrist, sports scientists, fitness coaches and a nutritionist along with him to Miami and they will all stop with the team until they are eliminated from the World Cup.
Much to Foster’s joy, England will be allowed tomato ketchup and brown sauce - both banned under Fabio Capello - during the tournament.
“We are allowed (ketchup and brown sauce) now,” said the West Brom stopper, who will start against Ecuador on Wednesday.
“The food is amazing. There are seven or eight different stations of everything you could want.”