Heat Index and a September Running Unit
Mr. Calder teaches third-period high school physical education (36 students, 50 minutes) and has scheduled a three-week running unit for the first three weeks of September because the state fitness test is in October. The running takes place on an unshaded asphalt lot; the nearest water fountain is a two-minute walk inside the building. This week's forecast is 92°F with 60% relative humidity, with a heat index near 100°F by 1:00 p.m., when the class meets. The district heat policy says only that "outdoor activity should be limited in extreme heat," with no numbers attached. In the class are two students with asthma, one student with sickle cell trait, and several students who have not done sustained activity over the summer; one student is repeating the class. Students are still wearing street clothes because the PE uniform order has not arrived. Last September, two students became dizzy during a similar unit.
1. How should Mr. Calder decide whether and how to hold class outside today? Include the information he needs and what he should do if the heat index is at or near 100°F.
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He should not rely on the forecast alone, and he cannot rely on a policy with no numbers. Before class he should get the current heat index - or better, the WBGT, which includes solar load - and take a reading in the actual setting. Asphalt in direct afternoon sun can be far hotter than the air temperature and radiates heat at ankle level, so the microclimate on that lot is worse than the reported index.
He should call the athletic director or district office to ask whether a numeric threshold exists, and if it does not, apply a defensible scale: below roughly 90–95°F heat index, normal precautions; roughly 95–104°F, reduce intensity and duration, shorten intervals, provide shade and water breaks at least every 15 minutes, and remove extra clothing; at or above about 104°F, move indoors or cancel outdoor activity. With today's index near 100°F, that means move the lesson indoors if any space exists; if not, shorten the outdoor portion, use intermittent activity with rest, keep students in whatever shade is available, and get water to the field rather than sending students on a two-minute walk.
He also needs the emergency plan settled before class: who calls 911, where the AED is, and how a student would be cooled - cold water, ice towels, fanning - while waiting. Document the decision and the reading.
2. Which students are at elevated risk and what individualized precautions are warranted?
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The students with asthma may bronchoconstrict in hot, humid air with high ventilation rates and poor air quality; confirm that reliever inhalers are accessible under district policy (including self-carry), give them a gradual warm-up, offer a walk/jog option, and watch for coughing, wheezing, or chest tightness.
The student with sickle cell trait is at risk of exertional sickling during high-intensity work combined with heat and dehydration. Keep intensity moderate and interval-based, enforce hydration, allow rest, and stop immediately for muscle cramps, back pain, or unusual shortness of breath - sickling can present as cramping and muscle breakdown rather than simple collapse. That student should never be pushed to exhaustion, especially in the first weeks.
The deconditioned and repeating students need the most gradual progression because their cardiovascular and thermoregulatory systems are the least acclimatized; heat acclimatization takes roughly one to two weeks of repeated exposure. Students in street clothes cannot cool well and may avoid sweating in khakis; a change of shirt and a water bottle should be a class requirement. Any student with a health plan - diabetes, cardiac condition, seizure disorder - should have that plan reviewed before heat exposure, and all students should be taught the warning signs of heat illness.
3. Design the first 10 days of the unit to build fitness while reducing heat illness risk.
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The first ten days should build heat tolerance and an aerobic base, not test fitness.
Days 1–3: 20–25 minutes of intermittent walking and jogging, one minute work and one minute walking, six to eight repetitions, with a mandatory water break after every two repetitions, plus a short teaching block on hydration, urine color, and the signs of heat illness (dizziness, headache, nausea, confusion, chills, or stopping sweating).
Days 4–6: two minutes work and one minute walking, six to eight repetitions, total under 25 minutes, staying at an intensity where students can talk in short sentences.
Days 7–10: three minutes work and one minute walking, five to six repetitions, adding a partner pacing task, but holding out-of-shade time to 15–20 minutes with rest in shade.
Use perceived exertion and the talk test rather than heart-rate targets, because heart rate drifts upward in heat at the same workload and will convince students they are working harder than they are. Reassess the heat index daily and reduce, shade, or move indoors when it rises. The October test can be prepared for with this progression - the goal is a base plus pacing skill, not heroic workouts in week one.