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The governing body of men's tennis said the rule, based on the internationally recognised Wet Bulb Globe Temperature (WBGT) index used to measure human heat stress in direct sunlight, had "clear thresholds" for cooling measures and suspension of play.

"The new heat rule provides a structured, medically supported approach to managing extreme heat, with the objective of safeguarding player health," the ATP said.

It added the rule would also improve conditions for fans, officials, ball persons and tournament staff.

If the WBGT reaches 30.1c or higher in the first two sets of a best-of-three-set singles match, a 10-minute cooling break after the second set can be requested by either player and will apply to both competitors.

During breaks, players can hydrate, change clothing, shower and receive coaching under the supervision of ATP medical staff, the governing body added. Play will be suspended when the WBGT goes past 32.2c.

World number-two Jannik Sinner's Shanghai title defence ended in agony in October when the Italian struggled to walk due to cramp in his right thigh before he retired in the deciding set of his third-round clash with Tallon Griekspoor.

At the same event, Novak Djokovic vomited during his encounter with Yannick Hanfmann while Holger Rune was heard asking an official during a medical timeout in his meeting with Ugo Humbert if players had to "die on court" amid the heat and humidity.

The need for a formal ATP heat rule had sprung up in August in Cincinnati when Arthur Rinderknech collapsed on court during a match in sweltering conditions, before handing Felix Auger-Aliassime the victory.

Previously, ATP regulations stated that decisions on the suspension of play due to adverse weather conditions - including extreme heat - lie with an onsite ATP supervisor who coordinates with medical teams at the venue as well as local authorities.

The new rule aligns the ATP with the WTA. The four Grand Slams have also formally implemented the rules that allow for extended breaks and match suspensions.

Several professional sports including soccer, Formula One and cycling have formal policies to deal with extreme weather.