OHIO (WOWO) — With a Heat Advisory in effect across Ohio and heat index readings expected to climb into the upper 90s and lower 100s, school athletic departments are using more than the thermometer to determine whether it is safe for student-athletes to practice outdoors.

The Ohio High School Athletic Association relies on wet bulb globe temperature, or WBGT, as a key measure for making decisions about practices and athletic activities during hot weather according to WTOL.

Unlike the standard heat index, WBGT is designed to account for the conditions athletes actually encounter while exercising outdoors.

The heat index generally combines air temperature and humidity to estimate how hot it feels in the shade. WBGT takes additional factors into account, including air temperature, humidity, wind conditions, the amount of solar radiation and the effects of cloud cover.

That can make a significant difference on an athletic field.

A football player practicing in direct sunlight while wearing a helmet and pads, for example, can face substantially more heat stress than someone standing in the shade under the same temperature and humidity conditions.

The same concern applies to athletes participating in soccer, cross country and other outdoor sports, as well as marching band members who may be practicing for hours in the heat.

The Ohio High School Athletic Association’s guidelines establish specific activity restrictions based on WBGT readings. Athletic departments are expected to monitor conditions before and during outdoor practices, with temperature and humidity readings taken every 30 minutes.

When the WBGT is below 79.7 degrees, normal activity is permitted. Athletes should receive three separate three-minute rest breaks during each hour.

Once the WBGT reaches 79.8 to 84.6 degrees, additional precautions are required. Athletes should receive three separate four-minute breaks each hour. Helmets and other equipment should be removed whenever athletes are not directly participating in practice, drills or competition and the equipment is not required.

At a WBGT of 84.7 to 87.6 degrees, restrictions become more significant. Practice is limited to two hours, and athletes should receive four separate four-minute breaks every hour.

Football players at that level are limited to helmets, shoulder pads and shorts. Schools are also encouraged to consider moving practices to later in the day, when conditions may be cooler.

The restrictions increase again when the WBGT reaches 87.8 to 89.7 degrees.

At that level, training is limited to one hour, with four separate five-minute breaks each hour. Additional conditioning is prohibited.

Football and lacrosse players cannot wear helmets, shoulder pads or other equipment under those conditions.

Once the WBGT rises above 89.8 degrees, outdoor workouts are prohibited.

Indoor workouts are also prohibited unless the facility is air-conditioned.

The increasingly restrictive guidelines are designed to limit the amount of heat stress placed on athletes while giving their bodies more opportunities to cool down.

That is particularly important because strenuous exercise can make it harder for the body to regulate its temperature. Protective equipment and heavy uniforms can trap additional heat, while direct sunlight can increase the body’s heat load.

Heat illness can develop quickly when athletes are exercising in extreme conditions, particularly when temperatures remain high overnight and the body has limited opportunity to recover.

The current weather pattern is adding to those concerns. According to the WTOL 11 Weather Team, peak heat index values are expected to reach the upper 90s to lower 100s through Wednesday, while overnight temperatures in the low to mid-70s could provide limited relief.

For coaches and athletic trainers, that means conditions need to be evaluated throughout a practice rather than simply checked at the start.

The WBGT approach also underscores why a weather forecast’s heat index number does not necessarily tell the entire story for an athlete.

Two locations with the same air temperature and humidity can present different risks depending on whether athletes are in direct sunlight, how much wind is available and whether cloud cover is providing relief.

The purpose of the OHSAA guidelines is not simply to cancel activities whenever temperatures rise. Instead, the system allows athletic departments to adjust the length and intensity of practices, increase rest periods, remove equipment and make other changes as conditions become more dangerous.

Access to water, shade and opportunities to cool down are also important parts of managing heat exposure.

For student-athletes, the rules are intended to provide a safety buffer before heat stress becomes a medical emergency.

As Ohio experiences some of its hottest conditions of the season, coaches, parents and athletes are being reminded that the number on the thermometer is only part of the equation according to WTOL.

The wet bulb globe temperature gives school officials a more comprehensive measurement of the heat athletes are experiencing — and helps determine when normal practice can continue, when additional precautions are needed and when outdoor activity has become too dangerous to continue.