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While news of Roger Federer's knee surgery was breaking, Novak Djokovic was sitting in a bath, sort of. The world No. 1 invented the Nole Challenge, which involves one minute in freezing water in Italy.

To complete the task, you must do the following:

Find freezing cold water outside in the winter

Wear only underwear

Put half your body in the water

Last at least one minute

He was joined by a pal, Constantine, who was far more submerged with nearly his entire body flat in the water. The duo were inspired by Wim Hof, a.k.a. the "Iceman". Hof is famous for enduring freezing temperatures.

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A post shared by Wim Hof (@iceman_hof)

Djokovic survived longer than his initial minute, saying, "Through various techniques (like breathing) we can calm ourselves enough to take on extreme conditions like this and more efficiently battle daily stress in our lives."

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