- New heat stress updated guidelines make calculation and use of the Heat Stress Index easier
- A Heat Stress Index takes into account not just air temperature but a range of factors
- Guidelines also set out when it safe for games to begin or resume
In 2025, World Rugby updated its heat and air quality guidelines, setting out all the measures to be taken to support players taking part in World Rugby competitions in hot conditions. The guidelines update the process for, and at what point water breaks are introduced, measures such as extending the half-time break or if a game needs to be postponed or suspended.
The new guidelines, written by Dr Grant Lynch and Dr Olly Jay of the University of Sydney, focus on a heat stress index rather than just the basic air temperature. The index runs between 0 and 250 with levels of heat stress determining what action will be taken.
World Rugby has purchased a number of EMU devices which measure all the elements which go into calculating the Heat Stress Index, including air temperature, humidity, wind speed and ground radiation. The readings are then put into the following categories:
- Low (0-99 Heat Stress Index) – teams follow standard practice
- Moderate (100 to 149) – players take on more fluids and reduce the amount of clothing worn
- High (150 to 199) – players to have a three-minute cooling break in each half. Team also to implement cooling strategies such as iced towels
- Very High (200 to 249) – half-time extended to 20 minutes
- Extreme (250+) – consider delaying or suspending the game
A handy calculator which tells you where measured conditions sit on World Rugby’s Heat Stress Index can be found here.
In the extreme case of a game being suspended or delayed the guidelines also set out exactly what conditions need to be met in order for the game to begin or resume:
- The Heat Stress Index must fall below 230 and remain below that level for 45 minutes
- Weather forecasts indicate a low risk of the Heat Stress Index rising above 250 for the next two hours if the game has started or three hours if it has not yet begun
- The Match-Day Doctor is happy that it is safe to play
The full guidelines are available on the World Rugby website here
