Regardless of your political views or thoughts on global warming, there’s no denying it’s been hot. Very hot. Here in central North Carolina, the temperature has been below 90 degrees only one day this month (88°F on August 11th). Temperatures exceeded 95°F on 8 out of the past 14 days with temperatures above 100°F for three. The rest of this week we expect high temperatures between 92°F and 101°F. And we’ve had soccer practices going on all month. As I noted earlier this month, we don’t have a hard and fast policy for excessive heat. We leave it up to the discretion of the coaches and parents and stress to the coaches the importance of frequent water breaks and less strenuous practices when the temperatures climb.

One reason we don’t have a more precise policy with thresholds and such is primarily due to the difficulty in measuring the true ‘heat effect’.

The Heat Index (HI) is commonly used to measure how hot it ‘feels’ and is often used to trigger heat advisories (HI of 105-114) and excessive heat warnings (HI of 115+). However, the Heat Index is an approximation. Here are some interesting facts[1] regarding the Heat Index:

  • The body is that of a 5′ 7″ Caucasian who weighs 147 pounds.
  • The person is wearing long pants and a short sleeve shirt
  • They are walking at 3.1MPH in a 6MPH breeze in the shade
  • If you are in direct sunlight, the Heat Index can be up to 15°F higher than calculated based on temperature and relative humidity.

As you can see – is it a subjective scale, but is better than nothing. The problem arises when organizations interpret the published ‘warning’ thresholds as applying to everyone.

A very common table you will see published is the “Heat Index/Heat Disorders” chart:

Category Classification Heat Index/Apparent Temperature (°F) General Affect on People in High Risk Groups
I Extremely Hot 130°F or Higher Heat/Sunstroke HIGHLY LIKELY with continued exposure
II Very Hot 105°F – 130°F Sunstroke, heat cramps, or heat exhaustion LIKELY, and heatstroke POSSIBLE with prolonged exposure and/or physical activity
III Hot 90°F – 105°F Sunstroke, heat cramps, or heat exhaustion POSSIBLE with prolonged exposure and/or physical activity
IV Very Warm 80°F – 90°F Fatigue POSSIBLE with prolonged exposure and/or physical activity

Seeing this, many organizations will see fit to limit activities when the Heat Index reaches 105°F or more. However, there is a very important thing to note. On the NOAA websites that list this table, they always note that it applies to people in High Risk Groups. Many other information sources often leave that key fact out. What are those high risk groups?

Elderly persons, small children, chronic invalids, those on certain medications or drugs (especially tranquilizers and anticholinergics), and persons with weight and alcohol problems are particularly susceptible to heat reactions, especially during heat waves in areas where a moderate climate usually prevails.

I’ve searched all over and cannot clarify what they mean by ‘small children’, but one would assume they mean babies and toddlers. Reading further NOAA information makes it clear that most heat warnings they issue are intended for high risk people. While healthy people can suffer from heat related illnesses, especially if they are dehydrated, I was unable to find a published Heat Index/Disorder chart for healthy children (say above the age of 4) or adults.

As you can see, this can make it VERY difficult to draft a sane policy to cancel outdoor sports activities based on heat index values. Consider this. If it is 88°F outside and the relative humidity is 80%, the Heat Index will be higher (and in the warning zone) than if it is 94°F and 50% relative humidity. Would you consider canceling your practice when it was 88°F outside?

A perfect case in point. Our local football league (pointy ball for you folks overseas) is run by the county and in response to concerns raised by a parent, they have published new rules for when football practices should be curtailed or canceled:

80°-90°F <70% RH – Observe those athletes susceptible to heat illness, especially those who are obese or have breathing conditions

80°-90°F >70% RH – All athletes should be under constant and careful supervision. Breaks every 20-30 minutes. Fluid replacement very important.

91°-95°F <30% RH – A shortened program of no more than 1 hour shall be conducted in shorts and t-shirts. Additional fluid replacement breaks are necessary.

96+°F or 91°-95°F >30% RH – Suspension of all outdoor practice/game activities.

So if the temperatures reach 96°F or higher, they won’t allow any practices, even with their pads and equipment removed. Yet at 90°F and 65% RH (Rule #1 in effect) the heat index is HIGHER than if it is 96°F and the RH is 40% or less – which is very common. When temperatures reach the 90’s, the relative humidity often drops below 50%. Do you see how bizarre a guideline like this is? Let’s translate the thresholds into Heat Index (HI) ranges and read it again. For comparison, I’m computing the Heat Indexes at the extremes (lowest humidity/lowest temp and highest humidity/highest temp). This will show the possible range of Heat Indexes and the associated guideline:

HI of 78-105 (80°F/0% – 90°F/69%) – Observe those athletes susceptible to heat illness, especially those who are obese or have breathing conditions

HI of 83-132 (80°F/71% – 90°F/100%) – All athletes should be under constant and careful supervision. Breaks every 20-30 minutes. Fluid replacement very important.

HI of 87-94 (91°F/0% – 95°F/29%) – A shortened program of no more than 1 hour shall be conducted in shorts and t-shirts. Additional fluid replacement breaks are necessary.

HI of 89-137 (91°F/31% – 95°F/85%) – Suspension of all outdoor practice/game activities. (Note I used 85% instead of 100% RH as it is difficult for humidity to stay any higher at that temperature due to haze and cloud cover effects)

Notice the problem? You could have a severe heat problem at stage two (careful supervision) with a heat index well above 100°F, yet you have to cancel practice when the Heat Index is no higher than the temperature (91°F) because of lower humidity (31%). Clearly our county athletic department didn’t think this one through too clearly. They would have been better off just going with pure Heat Index values to set their thresholds by. But even that is imperfect as a football player in pads is not the same as a 5′ 7″ 147lb person in the shade wearing a short sleeve shirt.

As you can see – there is no easy answer in terms of setting a hard and fast policy with thresholds and sticking to it. In the end you need to use common sense and keep it simple. You need to ensure your players get regular water breaks and are staying hydrated at home. If the temps continue to climb, you need to scale back the exertion level in your practice (more passing, less running/dribbling). And always be on the lookout for signs of heat stress. If your league has tents/canopies – put them out when temps hit a certain level to give parents and kids a little shade. Kids sensitive to heat? Send them home for a day off from practice. There’s no need to come out with tiered guidelines that use subjective value in their calculations.

Why make things so complicated when you don’t have to?

ADDING: One other aspect I didn’t mention is the Heat Index/Disorder tables talk about ‘prolonged exposure/physical activity’. They don’t specify what that amounts to, but consider this. Most soccer practices are 60-90 minutes. Figure on a really hot day you are taking water breaks every 10-15 minutes and those can take around 3 minutes. So when you look at it, you’re players are exerting themselves a total of 45-65 minutes. We’re not talking an 8 hour workday in the sun. Yes, you obviously have to be careful and it’s wise to alter practice plans in excessive heat. But it helps to look at this objectively and not freak out because the temperature has crossed that psychological 100 degree mark.

UPDATE: It looks like our county athletics folks got their policy from the North Carolina High School Athletic Association football guidelines. Except they’re guidelines, not hard and fast policy. They simply note the importance of monitoring players for signs of heat stress:

HOT WEATHER GUIDELINES: Precautions must be taken to prevent heat related problems. The following should be considered when scheduling practice: time of day, intensity level of practice, equipment worn, and environmental conditions. High temperature

and high humidity create a dangerous situation for athletes. However, a high humidity and low temperature can cause serious heat-related problems. Water should be made available in unlimited amounts throughout practice. Water/fluid replacement breaks are recommended each 20 or 30 minutes, depending on practice conditions.

And they include a version of that graduated table, but without the > 96F must cancel practice section and the T-Shirt/shorts recommendation kicks in at 90°F/50%. Hitting 50% humidity is much less common at 90°F+ than the 30% threshold the county chose. Instead the NCHSAA notes you may want to consider canceling practices in extreme temperatures. The county just took it a step further, tweaked the thresholds down to very low levels, and went from guidelines to policy.

I should add that I am NOT trying to minimize the danger of excessive heat. It seems every year we read about a high school student that collapses on the field in the heat because they were dehydrated or had a medical condition. My point in writing this is to highlight when organizations are being sensible with their policy or if they are overreacting. Most kids have horrible hydration habits. So instead of canceling practice because it hit 91 degrees when the humidity was 40%, we should be stressing the importance of proper hydration which means drinking plenty of liquids at home before practice, during practice, and again at home after practice. Simply canceling practices or sending kids to an indoor gym will never let them get acclimated to the heat. To me that puts them in more of a danger should they find themselves exerting themselves on a hot day.