Heat acclimatization is the two-week ramp that lowers a young athlete’s risk of exertional heat stroke, and the first practice of the season is where it matters most.
Two football players died in August 2026 after collapsing at or after that first practice. A 17-year-old senior lineman at Lake Travis High School in Texas collapsed at about 8 a.m. during the team’s first practice on August 10 and died three days later; the district described “complications from a medical emergency,” and the underlying cause hasn’t been released.
Eight days later, a 17-year-old junior at Pawnee Heights High School in Kansas collapsed during his team’s first practice and died that evening, with the cause undetermined pending autopsy.
Neither death has an official finding yet, and this article doesn’t attribute either one to heat. What both have in common is the day: practice one. That’s the day heat acclimatization exists for.
[TL;DR] Highlights and Key Takeaways
- Heat acclimatization is a 14-day ramp at the start of a warm-weather season; the Korey Stringer Institute guideline is the standard most programs follow.
- Days one through five: one practice a day, three hours maximum, no full gear, no live contact.
- Days six through fourteen: double sessions allowed on alternating days, five hours maximum on those days, full gear and contact from day six.
- Some state high school associations mandate the schedule; Texas now requires WBGT monitoring at every outdoor practice; most youth programs answer to no state rule at all.
- Four records decide a heat claim: the dated schedule, the practice log, the heat readings, and the emergency action plan.
- Cooling comes before transport. Cold-water immersion has to be on site before the first practice.
What heat acclimatization is
The term means the body’s adjustment to exercising in hot conditions. Over roughly one to two weeks of gradually increasing work, an athlete starts sweating sooner and more, the heart works less hard at a given effort, and core temperature rises more slowly. An athlete who hasn’t been through that adjustment carries a higher risk of exertional heat stroke, and the risk is highest in the first days of practice.
The guideline most programs follow comes from the Korey Stringer Institute at the University of Connecticut. It sets a 14-day acclimatization period at the start of any season that begins in warm weather.
The 14-day heat acclimatization schedule
The Korey Stringer Institute guidelines break the two weeks into two phases. The table summarizes that guideline; the lists below repeat it in words.
| Rule | Days 1 to 5 | Days 6 to 14 |
|---|---|---|
| Practices per day | One | One or two |
| Maximum practice time | 3 hours in the day, including warm-up, stretching, cool-down, and lifting | 3 hours per practice; 5 hours total on a double-practice day |
| Equipment | No full gear (football: helmets, then shoulder pads) | Full gear allowed from day 6 |
| Contact | No live full-contact drills | Live full-contact drills allowed from day 6 |
| Recovery rule | No double sessions | A double-practice day must be followed by a single-practice day or a rest day |
Days one through five:
- One practice per day. No double sessions.
- No more than three hours of practice in a day, counting warm-up, stretching, cool-down, and lifting.
- No full gear. For football, that means helmets only in the first days, then shoulder pads, with full pads held until day six.
- No live full-contact drills in contact sports until day six.
Days six through fourteen:
- Double-practice days are allowed, but each one must be followed by a single-practice day or a day of rest.
- On a double-practice day, no single practice runs over three hours and the two together stay under five hours.
- Full gear and full-contact drills are allowed from day six.
The schedule is built so the hardest days can’t come first. A football program that opens with two-a-days in full pads has skipped the part of the season the guideline was written to protect.
Did you know? The Korey Stringer Institute guideline holds full gear and live full-contact drills until day six of practice, and caps every practice at three hours including warm-up, stretching, cool-down, and lifting.
How state heat acclimatization requirements vary
The rules vary by state and by level, and a league should know which of three situations it’s in.
Some states mandate it for high school athletics. State athletic associations write acclimatization schedules into their handbooks, and a violation can bring sanctions on the program.
Texas went a step further for the 2026-2027 school year: beginning August 1, 2026, the University Interscholastic League moved wet bulb globe temperature (WBGT) monitoring from recommended to required. Under that rule, schools take a WBGT reading within 15 minutes before an outdoor practice and every 30 minutes during it, and at or above the regional threshold (79.7°F in Class 2 regions, 82°F in Class 3 regions) they must have rapid cooling available and modify the practice. Our guide to wet bulb globe temperature for coaches explains what the reading means and how to take one.
Some states recommend it without requiring it. The state association publishes the schedule, but there’s no penalty for a program that ignores it. Kansas, where KCUR reported the Pawnee Heights death as the state’s fifth football player to die around practice or conditioning since 2018, is one place where the question of what the state requires is now being asked out loud.
Did you know? KCUR counts 159 documented exertional heat stroke deaths in youth, high school, and college football between 1955 and 2021.
Under the high school level, almost no one requires it. Rec leagues, travel clubs, and middle school programs typically answer to no state athletic association. Their sanctioning body may publish heat guidance, but the league’s own policy is usually the only rule that applies. That’s the situation most youth programs are in, and it’s why the written plan matters more there, not less.
Why the heat acclimatization paperwork matters as much as the practice
When an athlete is seriously hurt, the question that follows isn’t whether the program cared about heat. It’s what the program can show it did. In a South Carolina case decided in July 2026, a jury found a school district grossly negligent over a football player’s heat stroke; the evidence centered on the records: whether a written heat plan existed, whether readings were taken, and whether cold-water immersion was available.
A youth program that follows the 14-day schedule but can’t prove it is in a weaker position than it deserves. Four records close that gap:
- The written acclimatization schedule, dated before the season starts, showing practice length, session count, and equipment by day.
- A practice log with the actual start and end time of each session and what equipment was worn.
- Heat readings for each outdoor practice, using a WBGT meter where the program has one, an app-based WBGT estimate where it doesn’t (an estimate, not a substitute for an on-site meter), or the heat index as a last resort, with the reading and the time.
- The emergency action plan, with the location of cold-water immersion equipment, the location of the nearest AED and who brings it to the field, and who is responsible for calling 911.
None of these takes more than a few minutes a day. All four have to exist before the first practice, because they can’t be reconstructed afterward.
A first-week heat acclimatization checklist
Before the first practice:
- The 14-day schedule is written, dated, and shared with every coach.
- Every coach knows the day-six line for full gear and full contact.
- A WBGT meter or heat-index source is assigned to a named person.
- Cold-water immersion is on site: a tub, water, and ice, not a plan to go get them.
- The emergency action plan names who calls 911 and who starts cooling.
- The AED location is confirmed, its battery and pads are checked, and a named person brings it to the field for every practice. To time how fast that AED reaches your farthest field, see the three-minute AED test.
During the first two weeks:
- One practice a day through day five, three hours maximum.
- Readings logged before and during practice.
- Any double-practice day followed by a single practice or rest.
- An athlete who shows confusion, stumbling, or collapse is cooled first and transported second. Cooling can’t wait for the ambulance.
Frequently Asked Questions
How long does heat acclimatization take?
The Korey Stringer Institute guideline uses 14 days: five days of single practices with no full gear, then nine days where double sessions are allowed on alternating days. The body’s adjustment continues past two weeks, but the highest-risk window is the first five days.
Is heat acclimatization required?
It depends on the state and the level. Some state high school associations mandate a schedule and can sanction programs that skip it; others only recommend one. Rec, travel, and middle school programs usually answer to no state rule at all, so their own written policy is what applies.
What is WBGT and do we need a meter?
Wet bulb globe temperature combines air temperature, humidity, sun, and wind into one reading, and it’s the standard state rules use. A handheld meter is the standard the rules assume; an app-based estimate is better than a plain thermometer but isn’t a substitute for an on-site reading. Either way, log the reading and the time.
Does acclimatization replace an emergency action plan?
No. Acclimatization lowers the odds of a heat emergency; the emergency action plan is what saves an athlete when one happens anyway. A program needs both, on paper, before the first practice.
When can players wear full pads?
Under the Korey Stringer Institute guideline, not before day six. The first five days are helmets and then shoulder pads only, with no live full-contact drills.
Can we hold two practices on one day during the first two weeks?
Not in days one through five. From day six on, a double-practice day is allowed if it’s followed by a single-practice day or a rest day, and the two sessions together stay under five hours.
What should a program do the moment an athlete shows signs of heat stroke?
Cool first, transport second. Confusion, stumbling, or collapse in the heat is treated as heat stroke until proven otherwise: call 911 and start cold-water immersion on site while the ambulance is on the way.
Does a signed waiver protect the league if a player suffers heat stroke?
Waivers vary by state and rarely cover gross negligence, and a missing heat plan is the kind of evidence a gross-negligence claim is built on. Treat the waiver as a backstop, never as the plan.
Does our league’s insurance cover a heat-illness claim?
Participant accident policies typically pay medical costs for a covered injury, and general liability responds to claims that the program was negligent. What the policy pays depends on its terms, so confirm both with the league’s agent before the season, not after.
Glossary of Terms
- Heat acclimatization: The body’s gradual adjustment to exercising in heat over one to two weeks, marked by earlier and heavier sweating, a lower heart rate at a given effort, and a slower rise in core temperature.
- Exertional heat stroke: A life-threatening condition in which core body temperature rises above about 105°F during exercise, with central nervous system changes such as confusion or collapse. It requires immediate cooling.
- WBGT (wet bulb globe temperature): A heat measure that combines air temperature, humidity, sun, and wind into one reading; the standard used in state athletic association heat rules.
- Heat index: A simpler measure that combines air temperature and humidity only. Less accurate than WBGT for outdoor practice because it ignores sun and wind.
- Cold-water immersion: Placing an athlete in a tub of cold water to lower core temperature quickly. The recommended first response to suspected exertional heat stroke.
- Emergency action plan (EAP): A written, venue-specific plan naming who calls 911, who starts cooling, where the equipment is, and how emergency crews reach the field.
- Double-practice day: Two separate practice sessions in one day. Not allowed in days one through five of acclimatization, and limited to alternating days after that.
- Full gear: For football, helmet and shoulder pads together with full pads. Held until day six under the guideline.
- State athletic association: The body that governs high school sports in a state and writes the rules member schools follow, such as the UIL in Texas or the KSHSAA in Kansas.
- Gross negligence: A legal finding that conduct fell far below the standard of reasonable care, which can defeat waivers and immunities that protect against ordinary negligence.
What heat acclimatization means for a league’s insurance
Heat illness is one of the most preventable serious injuries in youth sports, and it’s also one of the most litigated. A written plan, followed and logged, is the program’s best defense in a claim and one of the first things an underwriter asks about at renewal.
For how a heat-illness plan fits with a league’s accident and liability coverage, see Sadler Sports Insurance’s guide to heat illness prevention in youth sports.
Sources: Korey Stringer Institute heat acclimatization guidelines; University Interscholastic League heat stress policy, 2026-2027; KWTX and KCUR reporting on the August 2026 deaths; The State via AOL on the Richland County verdict. This article is general safety information, not legal or insurance advice; state rules change, and a program should confirm its own state association’s current policy.