Rectal Temperature Is the Only Reliable Way to Diagnose Exertional Heat Stroke on the Field

Most emergency action plans for heat illness are built around a single assumption: one athlete goes down, one medical responder takes charge, one call to 911 goes out. It is a reasonable starting point. It is also dangerously incomplete.

In recent years, coaches and athletic trainers have witnessed something that the standard EAP template was never designed to handle: multiple athletes collapsing from exertional heat stroke (EHS) during the same practice or event. When that happens, a plan built for one patient fractures immediately. Who gets the ice tub first? Who calls 911 when the athletic trainer is already immersed in cooling a critical athlete? Who monitors the second and third casualties while the first is being treated?

The hard truth: Exertional heat stroke is 100% survivable with proper care, according to research published in Current Sports Medicine Reports. The window to act is 30 minutes. A plan that collapses under the weight of two simultaneous casualties turns a survivable emergency into a preventable death.

This article is for coaches and athletic trainers who want to close that gap before it costs a life.

Multiple Casualties Are Not a Rare Edge Case

For years, the conventional wisdom in sports medicine held that heat stroke events were isolated incidents. One athlete, one response, one outcome. The data tells a different story.

Military surveillance data from Fort Benning, Georgia provides the most detailed picture of clustered heat casualties in an organized training environment. Over a five-year period, clusters of 10 or more heat illness casualties occurred on 19 separate days, with the largest single-day cluster reaching 20 casualties across seven different units. Of the 243 total casualties in those cluster events, 32 (13.1%) were diagnosed with heat stroke, not just heat exhaustion. These were life-threatening emergencies happening simultaneously across multiple locations.

Civilian athletics face the same risk pattern. Research on mass-participation endurance events published in peer-reviewed literature documents heat stroke rates as high as 3.7 per 10,000 starters in endurance running, with 78% of cases clustering on the three hottest days of competition. At a triathlon study tracking over 68,000 competitors, 12 athletes were diagnosed with EHS across 11 events, with multiple cases occurring during the same race.

Why Team Sports Are Particularly Vulnerable

In team sports, the risk of simultaneous casualties is structurally higher than in individual sports. Every athlete on a football field, soccer pitch, or track is:

Exercising at similar intensity levels
Exposed to the same ambient temperature and humidity
At the same stage of acclimatization (or lack thereof)
Often wearing similar equipment that traps heat

This shared exposure means that when conditions are dangerous enough to take down one athlete, they are likely dangerous enough to take down several. American football has the highest incidence of heat illness of any team sport, ranging from 0.6 to 41.9 cases per 10,000 athlete-exposures. EHS-related death rates in football are also the highest of any sport, with 47 of 63 EHS-related deaths in football between 1995 and 2017 occurring at the secondary school level. Ninety percent of those deaths happened during practice, not competition.

The preseason window is the highest-risk period. EHI rates during preseason are 9.8 times higher than during the regular season (1.45 vs. 0.15 per 10,000 athlete-exposures). This is exactly when athletes are least acclimatized, coaches are pushing conditioning hardest, and medical resources are often thinnest.

Where Standard EAPs Break Down

The NATA Position Statement on Emergency Action Plan Development is clear: an EAP should not be injury or illness specific, and it must delineate a chain of command with anticipated roles for all available personnel. Most programs read that guidance and build a plan. The problem is that most of those plans implicitly assume a single-patient event.

Here is what a standard EAP response looks like for one EHS casualty:

First responder recognizes EHS (altered mental status, core temp above 104°F)
Athletic trainer initiates cold water immersion (CWI) in the ice tub
A second person calls 911 and directs EMS to the scene
AT monitors rectal temperature until it drops below 102°F (38.9°C)
EMS transports athlete to hospital

This works. Every role is covered. Now add a second athlete going down while the first is still in the tub.

The Multi-Casualty Failure Points

When a second or third athlete collapses simultaneously, most standard EAPs hit three critical failure points:

Failure Point	What Happens	Why It Is Dangerous
Single cooling resource	Only one ice tub is available; second athlete waits	EHS requires core temp below 102°F within 30 minutes of collapse. Every minute of delay increases organ damage risk.
Undivided AT attention	The AT cannot safely monitor two immersed athletes at once	Continuous rectal temperature monitoring and CNS status checks are required throughout cooling.
Communication breakdown	The person who called 911 is now managing the scene; nobody has communicated that there are multiple critical patients	EMS may arrive prepared for one patient and be caught off guard by two or three.

The NATA Inter-Association Task Force on Emergency Health and Safety specifies that the EAP coordinator must delineate a chain of command with roles for all available personnel. In a multi-casualty scenario, that chain of command needs to be pre-assigned, not improvised on the field while two athletes are in crisis.

What a Multi-Casualty Heat EAP Must Include

Building a heat EAP that holds up when multiple athletes go down requires addressing five specific gaps that single-patient plans leave open.

1. Pre-Assigned Roles for Every Scenario

Every person on the sideline, in the training room, or on the coaching staff needs a defined role before an emergency starts. The NATA EAP Position Statement recommends that the EAP coordinator delineate a chain of command with anticipated roles for all available personnel, and that this chain must not rely solely on health care team members.

For a multi-casualty heat event, pre-assigned roles should include:

Primary medical responder: The AT or most qualified person on-site. Manages the most critical patient.
Secondary responder: A trained coach, assistant AT, or team physician who manages the second casualty until additional help arrives.
EMS caller: A designated individual whose only job is to call 911, communicate the number of casualties, and guide EMS to the scene.
Equipment runner: Retrieves additional cooling supplies (ice bags, towels, a second tub if available) immediately upon the second casualty being identified.
Scene controller: Keeps other athletes away from the area, prevents panic, and maintains a clear path for EMS.

These roles must be practiced, not just written down. Run a tabletop drill. Walk through what happens when two athletes collapse within five minutes of each other.

2. Multiple Cooling Resources On-Site

A single ice tub is not enough. The NATA Consensus Statement on Heat Illness is explicit: cold water immersion (CWI) at approximately 35°F to 58°F (1.67°C to 14.5°C) is the gold-standard treatment for EHS. Alternatives, including ice towel rotation, cold water spray with fans, and ice packs over major vessels, are acceptable when immersion is not possible, but they cool significantly more slowly.

Programs should have, at minimum:

One dedicated ice tub per 25 to 30 athletes at high-risk practices (preseason, extreme heat days)
Backup cooling supplies staged and ready: multiple bags of ice, large plastic tarps or kiddie pools that can be converted into emergency cooling stations, and a continuous water source
Ice towels pre-staged in coolers so they are ready for immediate rotation on a second or third casualty

The goal is to begin cooling every EHS athlete within minutes of collapse, not to wait for the first tub to free up.

3. Communication with EMS Before the Season Starts

The NATA Inter-Association Task Force recommends that EAPs be developed in concert with local EMS providers. This is not a formality. It is an operational necessity.

Before preseason begins, contact your local EMS agency and communicate:

The location of your facility and the fastest vehicle access route
That your program uses “cool first, transport second” protocols, so EMS should stand by on-site during cooling rather than loading athletes immediately
The maximum number of athletes on-site during high-risk practices, so EMS can pre-plan for a potential multi-casualty response

When you call 911 during a multi-casualty event, the dispatcher needs to know immediately: “We have multiple athletes with suspected exertional heat stroke. We are cooling on-site. We need multiple units.” That message, delivered clearly, changes the EMS response from a single ambulance to a mass casualty dispatch.

4. Environmental Monitoring as a Trigger

The best multi-casualty plan is the one that prevents the event from happening. The NATA Youth Sports Task Force guidelines recommend using a wet-bulb globe temperature (WBGT) device, heat index chart, or local weather data to assess whether it is safe to exercise before every outdoor practice.

When WBGT or heat index reaches threshold levels, the EAP should automatically trigger heightened protocols:

Increase rest-to-work ratios
Reduce equipment and protective gear
Station a dedicated monitor whose only job is watching athletes for early signs of heat illness
Pre-fill ice tubs before practice begins, not after the first athlete goes down

Critical insight: Multiple simultaneous casualties almost always occur when environmental conditions are at their worst. Having your multi-casualty response resources already staged when the heat index is extreme is the difference between a managed emergency and a chaotic one.

5. A Documented Triage Protocol

When two or more athletes show signs of EHS at the same time, the responding team needs a pre-established triage framework. World Athletics’ Emergency Care guidelines recommend the standard ABCDE primary survey (Airway, Breathing, Circulation, Disability/neurologic status, Exposure) for all casualties, followed by rapid resuscitative measures.

For heat-specific triage in a multi-casualty scenario:

Identify the most critical patient first. An athlete who is unconscious or has no detectable pulse takes priority over one who is confused but responsive.
Begin cooling on all suspected EHS casualties simultaneously using whatever resources are available. An athlete in an ice towel wrap is being cooled. An athlete waiting with no intervention is losing the 30-minute window.
Assign one monitor per athlete once cooling is initiated. Core temperature must be checked continuously via rectal thermometer. Cooling stops when temperature reaches approximately 101°F to 102°F (38.3°C to 38.9°C).
Do not transport until cooled, unless the athlete has a life-threatening airway, breathing, or circulation issue that cannot be managed on-site. The “cool first, transport second” mandate applies to every EHS patient, not just the first one treated.

The Bottom Line for Coaches and Athletic Trainers

The assumption that only one athlete will go down at a time is not a reasonable baseline anymore. It is a planning failure waiting to become a tragedy.

Exertional heat stroke is survivable. Every single case, with the right response. The 30-minute cooling window is not a guideline; it is a biological deadline. When two or three athletes hit that deadline at the same moment, a plan built for one will fail them.

The standard of care is clear: “Cool first, transport second” applies to every EHS patient simultaneously. Your EAP must be built to execute that standard for multiple athletes at once, with pre-assigned roles, staged equipment, and EMS partners who know what to expect.

Audit your current EAP against these five questions:

Does your plan name a secondary responder for a second simultaneous casualty?
Do you have enough cooling resources on-site to begin immersion or aggressive cooling on two athletes at the same time?
Have you contacted your local EMS agency before this season to walk through a multi-casualty heat scenario?
Does your EAP include an environmental trigger that stages resources before the first athlete goes down?
Has your staff practiced a two-casualty drill, not just a one-casualty drill?

If any answer is no, the plan is not finished. Review the NATA Position Statement on EAP Development and the NATA Inter-Association Consensus Statement on Heat Illness as the authoritative frameworks for building a plan that actually holds up when the worst-case scenario stops being hypothetical.

If you need a faster starting point, use the free EAP Builder to draft a plan you can review, customize, and test with your staff before the next hot practice.

There is a thermometer in your training kit right now that will give you the wrong reading when an athlete is in crisis. If you are using an oral, tympanic (ear), temporal, axillary (armpit), or forehead thermometer to assess a heat-collapsed athlete, the number on that device is not an accurate reflection of what is happening inside the athlete’s body. It may be off by several degrees. In a condition where the difference between 103°F and 106°F determines whether an athlete lives or dies, that gap is not a rounding error.

This is not a fringe opinion. It is the explicit, evidence-based position of both the National Athletic Trainers’ Association (NATA) and the American College of Sports Medicine (ACSM): rectal temperature is the only valid method for measuring core body temperature in an exercising or recently exercised individual. Every other common device is clinically unreliable in this context.

The stakes: Exertional heat stroke (EHS) is defined by two criteria: central nervous system (CNS) dysfunction and a core body temperature above 40.5°C (105°F). If you cannot accurately measure core temperature, you cannot accurately diagnose EHS. And if you cannot diagnose it, you cannot treat it in time.

Most coaches and athletic trainers know they should have a rectal thermometer on the sideline. Fewer understand exactly why every alternative fails, or what to do when a rectal temperature cannot be taken immediately. This article answers both questions, grounded entirely in peer-reviewed research and current clinical guidelines.

Why Core Temperature Is Different from Skin Temperature During Exercise

To understand why common thermometers fail, you need to understand what happens to the body’s temperature distribution during intense exercise in the heat.

When an athlete is working hard, the body redirects blood flow toward the working muscles and toward the skin to facilitate heat dissipation through sweat evaporation. This creates a significant temperature gradient: the core (the deep organs, including the brain, heart, and liver) heats up rapidly, while the skin, mouth, ear canal, and armpit may actually read cooler than the true internal temperature because blood is being shunted away from those surfaces or because sweat is evaporating and cooling the skin.

This is the core problem: The sites where common thermometers measure temperature are precisely the sites that decouple from core temperature during exercise. Rectal temperature, by contrast, reflects the temperature of the deep venous blood returning from the working muscles and remains tightly correlated with true core temperature even during intense exertion.

What the Research Confirms

Two landmark peer-reviewed studies published in the Journal of Athletic Training and indexed on PubMed/NIH tested multiple common thermometer types against rectal temperature as the criterion standard during outdoor and indoor exercise in the heat. The findings were consistent across both studies:

Oral thermometers: Invalid. Underestimated core temperature by an average of 0.60°C (1.08°F) at rest, with the gap widening significantly as hyperthermia increased. At the highest recorded rectal temperatures, oral devices were off by more than 4°F.
Tympanic (ear canal) thermometers: Invalid. These devices do not contact the tympanic membrane directly; they measure infrared radiation from the ear canal, which is influenced by airflow, ambient temperature, and skin blood flow.
Temporal (forehead) thermometers: Invalid. Forehead skin temperature is heavily influenced by sweating and ambient air, both of which are present in every outdoor athletic emergency.
Axillary (armpit) thermometers: Invalid. Axillary temperature measured an average of 1.4°C (2.6°F) lower than rectal temperature even before exercise began, a gap that widens during and after exertion.

“No other field-expedient methods of obtaining core body temperature (eg, oral, axillary, tympanic, forehead sticker, temporal) are valid or reliable after intense exercise in the heat, and they may lead to inadequate or inappropriate treatment, thereby endangering a patient’s health.” — NATA Position Statement on Exertional Heat Illnesses

The ACSM Expert Consensus Statement is equally direct: “Ear (ie, aural), oral, skin, temporal, and axillary temperature measurements should not be used to diagnose or distinguish EHS from exertional heat exhaustion.”

The Real-World Consequence of an Inaccurate Reading

The clinical danger of using an invalid thermometer is not theoretical. Consider what actually happens when an athletic trainer relies on an oral thermometer to assess a collapsed athlete.

An athlete collapses during a summer football practice. She is confused and combative, which is a classic CNS symptom of EHS. The athletic trainer takes an oral temperature: it reads 101.8°F. That reading, if trusted, suggests heat exhaustion rather than heat stroke. The treatment decision changes. Cold water immersion may be delayed or skipped in favor of rest, fluids, and monitoring.

What the oral thermometer did not capture: the athlete’s actual rectal temperature was 106.2°F. She had EHS. The 30-minute cooling window was already running.

This scenario illustrates why the NATA position statement is explicit that a rectal temperature assessment must be obtainable under all circumstances in which EHS is possible. The consequence of misdiagnosis is not a delayed recovery. It is organ damage, multi-organ failure, or death.

Why the Gap Gets Worse at Higher Temperatures

The most alarming finding from the peer-reviewed literature is that the inaccuracy of oral thermometers does not stay constant. It increases as the athlete’s true core temperature rises. A systematic review published in the Journal of Athletic Training found that the mean bias between oral and rectal temperature exceeded 4°F (2°C) when rectal temperature reached the critical range above 104°F. In other words, the hotter the athlete actually is, the more the oral thermometer underestimates the danger.

This is the opposite of what you need from a diagnostic tool in an emergency. The device becomes least reliable precisely when accuracy matters most.

How to Take a Rectal Temperature in an Athletic Setting

The most common reason athletic trainers and coaches avoid rectal thermometry is discomfort with the procedure, not disagreement with the science. That barrier is understandable, but it is not a clinical justification for using an invalid method. The NATA’s position statement gives this a Strength of Recommendation A: under all circumstances where EHS is possible, rectal temperature assessment must be obtainable.

Here is the practical protocol, consistent with NATA guidelines:

Equipment Required

A standard flexible-tip rectal thermometer (digital)
Lubricating jelly
Gloves (non-latex preferred)
A privacy screen or towel for modesty

Procedure

Position the athlete on their side (lateral decubitus position) or on their stomach. If the athlete is in the ice tub, remove them briefly only if necessary; rectal temperature can be monitored continuously with the thermometer in place during cold water immersion.
Apply lubricating jelly to the tip of the thermometer.
Insert the thermometer approximately 4 to 5 cm (about 1.5 to 2 inches) into the rectum.
Hold in place until the device registers. Digital thermometers typically take 10 to 60 seconds.
Record the reading and continue monitoring every few minutes throughout cooling.
Stop active cooling when rectal temperature drops to approximately 101°F to 102°F (38.3°C to 38.9°C), per NATA and ACSM guidelines. Do not use the thermometer reading as a reason to delay initiating cold water immersion if EHS is clinically suspected.

Addressing the Consent and Privacy Concern

The NATA position statement acknowledges that parents, administrators, and athletes may be uncomfortable with rectal thermometry. The recommended approach is proactive education before the season begins. When athletes, parents, and administrators understand in advance that this is the medically required standard of care for a potentially fatal condition, resistance is significantly reduced.

“Parents, administrators, and athletes should be educated prior to the season that rectal thermometry is the standard of care for diagnosing EHS.” — NATA Position Statement on Exertional Heat Illnesses

Building this education into your pre-season athlete and parent orientation is not optional. It is part of the EAP.

What to Do When a Rectal Temperature Cannot Be Taken Immediately

There will be situations where rectal thermometry is not immediately possible: the athlete is combative, no privacy screen is available, or the thermometer is not yet on the scene. The ACSM Expert Consensus Statement addresses this directly, and the answer is clear: do not wait.

“Body cooling should take priority if a rectal temperature cannot be measured immediately, but a temperature measurement will eventually be needed to determine an end point for active cooling.” — ACSM Expert Consensus Statement on Exertional Heat Illness

In practice, this means:

Situation	Action
Rectal thermometer is available and athlete is cooperative	Take rectal temperature first, then begin cooling
Rectal thermometer is available but athlete is combative	Begin cold water immersion immediately; obtain rectal temperature as soon as safely possible
Rectal thermometer is not immediately on scene	Begin cooling based on clinical signs (CNS dysfunction + collapse in heat); retrieve thermometer; do not delay cooling to find a thermometer
EMS has arrived and is ready to transport	Insist on “cool first, transport second”; cooling must continue until rectal temperature is confirmed below 102°F

The Clinical Signs That Justify Immediate Cooling Without a Temperature

The ACSM consensus statement identifies the following as indicators that an athlete should be managed as an EHS casualty and cooled immediately, even before a rectal temperature is confirmed:

Persistent mental status changes (confusion, disorientation, combativeness, loss of consciousness)
Collapse during or after exercise in hot conditions
Seizure activity
Recurrent vomiting with altered mental status
Loss of ambulatory function (inability to walk normally)

The key principle: When in doubt, cool. The risk of aggressively cooling an athlete who turns out to have heat exhaustion rather than EHS is minimal. The risk of withholding cooling from an athlete who actually has EHS is catastrophic.

The Thermometer Checklist: What Belongs in Your Kit

Before every high-risk practice (preseason, extreme heat days, any session with a heat index above 103°F), the following should be confirmed in your medical kit:

Rectal thermometer: At least one flexible-tip digital rectal thermometer, confirmed to be functioning
Lubricating jelly: Stored with the thermometer, not across the facility
Gloves: Non-latex, immediately accessible
Privacy screen or large towel: Pre-staged, not something you have to search for during an emergency
Documentation: A way to record temperature readings over time during cooling (a simple notepad works)

What does not belong on this list for EHS diagnosis: oral thermometers, ear thermometers, temporal scanners, forehead strips, or any device that does not measure rectal temperature. These may have other uses in your kit, but they are not valid tools for diagnosing or monitoring exertional heat stroke.

If your current EAP does not specify rectal thermometry as the required assessment method for suspected EHS, it is not complete. The NATA’s EAP development guidelines require that EAPs specify the equipment needed for each emergency scenario. For heat stroke, that equipment list starts with a rectal thermometer.

Use the free EAP Builder at nationalstaycoolday.com/eap-builder to build or update your heat emergency protocols, including the thermometry requirements, cooling procedures, and role assignments your plan needs to meet the current standard of care.