MLS Hydration Breaks Explained

MLS Hydration Break

EDITORIAL – Hydration breaks have been implemented in soccer for several years how including Major League Soccer. The 2014 World Cup match between the United States and Portugal was the first time a hydration break happened in the World Cup. Lets take a look at the rule and what goes into MLS hydration breaks.

MLS Hydration Breaks Explained

The league’s 2019 competition guidelines explain hydration breaks as follows:

HYDRATION BREAKS: MLS mandates the use of hydration breaks if the WetBulb Globe Temperature (WBGT) measures 82 degrees Fahrenheit or higher. The referee can, at any time, implement a discretionary hydration break in cases in which player safety is determined to be at risk.

The Fourth Official will be responsible for reading the WBGT at the kickoff spot at the conclusion of the pre-match warmup. A reading will occur after the whistle blows for the end of the first half to determine if a hydration break is needed.

Implementation and control of the breaks will be managed solely by the referee:

– Each break will last up to three minutes in length and held approximately 30 minutes into each half (around the 30th and 75th minute respectively).
– The ball must be out of play for the break to commence.
– The clock will continue to run and all time allotted for the break will be added to stoppage time.

So that’s the rule, but we need to define the WBGT: A measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover.

WBGT is considered a better metric for determining if physical activity becomes difficult or risky in terms if injury or fatigue. One key difference between WBGT and heat index is that heat index is measured in the shade.

So WBGT does not take into account the roofed/shaded parts of the stadium with one exception. The rule clearly states that the fourth official must take the reading of the WBGT at the kickoff spot (the center circle).

So for a stadium like Mercedes-Benz Stadium in Atlanta the WBGT will be inherently in the shade most of the time unlike say BBVA Compass Stadium in Houston which will not.

If you want to learn more about the math, click here. Here’s the basics of how the actual WBGT is calculated after the measurements are taken:

WBGT = 0.7*Tw + 0.2*Tg + 0.1Td

Tw: Natural wet bulb temperature, which indicates humidity
Tg: Globe thermometer temperature, which indicates radiant (read: sun) heat
Td: Dry bulb temperature, which indicates ambient air temperature

There are plenty of variations of devices that do the measurements and math for you. So the fourth official has one of these instruments. They take a measurement at center circle. If the meter reads 82 deg F or higher, then that half will have a hydration break 30 minutes in.

Hydration breaks help the players with dehydration and prevent injury, thus being less Draconian and helping to protect the integrity of the competition.

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