The squad is in a training camp in Girona, Spain, as they practice ahead of the tournament in the USA, Canada and Mexico next year.

They are taking part in fitness tests on exercise bikes inside the tents and their recovery afterwards will be looked at.

It comes as manager Thomas Tuchel believes his players may struggle with the intense climate during the World Cup - which kicks off on June 11 and ends on July 19 next year.

It has been warned that temperatures could exceed "potentially dangerous levels" at 14 of the 16 stadiums that are being used to stage matches.

Because of this, he will travel to the United States to assess what the weather conditions are like at "three in the afternoon" and work out the best way to keep the team hydrated.

Tuchel, whose team face Andorra in a World Cup qualifier and Senegal in a friendly this month, said: "It is important to see matches now in America, and in Miami at three in the afternoon.

"I will see that. How it looks, and we need to understand how to cool the players down, to drink. What our options are.

"Let's see because it is after the season, so it will be very similar. The actual experience is for the players, but I have done pre-season there in Orlando and I will be very surprised if we do not suffer. Suffering is one of the headlines for this World Cup."