Thermal physiology
Exertional Heat Stroke in Elite Sport: The Risk Your Heat Policy Does Not Cover
Three young forwards have now collapsed at training and died in five and a half years. Exertional heat stroke is one of the most predictable conditions in sport, and almost all of the prevention happens in the diary, the measurement and the session plan.
Exertional heat stroke in sport is prevented by controlling two things: the heat an athlete gains from the environment, and the heat they generate through work. That means four decisions, all made before a session starts. Measure wet bulb globe temperature at the venue rather than relying on a forecast. Design the session so that work to rest ratio, contact load and time of day match the conditions. Build seven to fourteen days of progressive acclimatisation into pre-season and into every athlete arriving from a cooler climate or returning from illness. And write the environmental trigger points and their session modifications down in advance, with a named person authorised to invoke them without asking the head coach.
Three deaths in five and a half years
In November 2020, Keith Titmuss collapsed after a pre-season session with the Manly Warringah Sea Eagles at Narrabeen. He was 20 and had just been promoted into the top 30 squad. The 2024 coronial inquest found he died of exertional heat stroke. That matter remains before the courts and I have no interest in commenting on fault.
On Friday 10 July 2026, Luqobo Makwedini fell ill at the end of a morning session with AS Béziers Hérault in the south of France, during a European heatwave. He was 20 years old, a South African tighthead prop who had come through Wynberg Boys' High in Cape Town and joined the Béziers academy the previous season. He stood 1.76 metres and weighed 119 kilograms. He was taken to hospital and died a few hours later. French reports suggested a cardiac arrest. His family have said they were told the cause was severe heat stroke. No official cause has been confirmed.
Three and a half weeks after that, on Monday 3 August, Saimoni Vunilagi finished a training session in Fukuoka and showed symptoms consistent with severe heat stroke. He died on Friday 7 August, aged 26. He was 196 centimetres and 117 kilograms, and had joined Kyuden Voltex only weeks before. Fukuoka reached around 35 degrees that day.
Three young forwards, all of them among the largest athletes at their clubs. Three collapses at training rather than in competition. Five and a half years after an Australian coroner set out in detail what exertional heat stroke does and how it is prevented, two more inside a month.
What I am interested in is the window before each of those sessions began, because that is where this condition is won or lost.
Why is exertional heat stroke preventable?
Heat illness has a reputation as a freak event. It is closer to the opposite. Core temperature is governed by two inputs: the heat an athlete generates through work, and the heat the environment allows them to shed. Both are measurable, both are known in advance, and both are within a club's control. Very few hazards in sport are that tractable. The reason heat still kills people is that most organisations manage only one of the two inputs, and manage it with a weather forecast.
Why is the cause so often unclear?
In two of the three cases above, the cause was contested or unconfirmed. That is not unusual, and it is worth understanding why.
Exertional heat stroke and cardiac collapse are not clean alternatives. Severe hyperthermia places extreme demand on the cardiovascular system, reduces the volume of blood available to the heart as flow is diverted to the skin, and can itself produce a cardiac event. An athlete who collapses at the end of a hot session may present in a way that looks cardiac to everyone standing over them, whether or not heat is what put them there.
What separates the two is a core temperature reading taken at the point of collapse. Rectal measurement is the only field method accurate enough to settle it, because oral, tympanic and forehead devices measure peripheral tissue that lags badly and can read normal in an athlete whose core is above 41 degrees. That reading is almost never taken. Once the athlete has been moved, cooled in transit, or resuscitated, the information is gone and cannot be recovered afterwards.
The practical consequence is that heat is almost certainly under-counted in sport, and that any argument for prevention which depends on proving the cause afterwards will always arrive too late. The controls set out below reduce the risk of both outcomes, which is why they are worth putting in place regardless of what any individual investigation concludes.
How should a club measure heat risk?
Air temperature is a poor description of thermal hazard. It ignores humidity, radiant load from the surface, and air movement. When humidity is high, sweat runs off the skin instead of evaporating, and evaporation is where nearly all of the cooling happens during hard work. The athlete loses fluid without losing heat. That is why 30 degrees and humid is more dangerous than 35 degrees and dry, and why a forecast maximum tells you almost nothing about what a player is standing in.
Wet bulb globe temperature, usually written as WBGT, captures all four variables in a single number. A handheld instrument costs a few hundred dollars, and the discipline it enforces matters more than the device. Take the reading at the venue, on the surface being used, at the time the session runs. Synthetic turf on a clear afternoon can sit well above the air temperature. A ground with no breeze behaves differently to one with an open aspect. A regional forecast describes none of this.
The same logic applies indoors, which is where heat policies most often fail. A short gym session after a long outdoor session can carry the higher risk of the two, because moving inside feels like relief and because almost every heat policy in the country is written around outdoor conditions. Poorly ventilated indoor spaces in summer hold heat and humidity with no radiant relief and no air movement, and nobody thinks to measure them.
How does session design change heat risk?
You cannot change the weather. You can change everything else, and this is the half most clubs leave untouched.
Metabolic heat production is set by session design. A continuous conditioning block, contact work in protective gear, and repeated maximal efforts with short recoveries all generate far more heat than skills work at the same air temperature. Two sessions run in identical conditions can carry entirely different risk depending on work to rest ratio, total duration, whether the session is stacked on top of another one, and what time of day it is scheduled.
Practically, that means the controls with the most leverage are the least dramatic ones. Move the session earlier or later. Shorten the blocks and lengthen the recoveries. Take the contact out and keep the skills in. Split a ninety minute session into two shorter ones. Reduce the load rather than cancelling, so that modification stays a live option instead of an all or nothing decision that nobody wants to make.
How long does heat acclimatisation take, and who needs it?
Seven to fourteen days of progressive, controlled heat exposure produces earlier onset of sweating, a higher sweat rate, plasma volume expansion, lower heart rate and lower core temperature at the same workload. The effect size is substantial and it is achievable inside any pre-season. It also decays within a couple of weeks of the exposure stopping, which means it has to be planned rather than assumed.
The value of understanding this is that it makes the highest risk people in a squad entirely predictable before anyone sets foot on the field. Athletes returning from the off-season. New arrivals from a cooler climate or hemisphere. Anyone coming back from illness, particularly a febrile one. Athletes carrying the most mass, who produce more metabolic heat in absolute terms and have proportionally less body surface to shed it through. And anyone with a history of prior heat illness, which is the strongest single predictor there is.
That list is knowable on day one of pre-season. Individual acclimatisation plans and graduated first fortnights for the people on it will prevent more heat illness than any intervention applied on the day.
Who should decide to modify or stop a session?
The failure mode is rarely ignorance. It is a decision being made in the moment, by someone with a programme to complete, under conditions that make the decision hardest.
What survives that pressure is a plan written in advance. Set the environmental bands and write the specific modification that applies at each one, so that the person on the ground is implementing a decision rather than making one. Name who holds the authority to invoke it and make sure they can do so without negotiating with the head coach. Rehearse it once so it is not novel the first time it matters.
Does hydration prevent heat stroke?
Hydration is worth managing, and it is oversold as the answer. Fluid replacement supports sweating and cardiovascular function, and it does not prevent exertional heat stroke on its own. An acclimatised athlete in a well designed session in measured conditions is protected. A well hydrated one in a badly scheduled session is not.
Prevention is never total, so a club still needs the capability to recognise and cool an athlete rapidly on site. That capability should be the last line rather than the plan.
Three young men in five and a half years, two of them inside a month, in a condition where the decisive choices were made in a calendar, on a session plan, and with a measurement that either was or was not taken. A coroner has already published what needed to happen. That is unglamorous work, and it is the work that means nobody has to be the person standing over a collapsed athlete in the first place.
Frequently asked questions
What is exertional heat stroke?
Exertional heat stroke is a life threatening condition in which core body temperature rises past roughly 40 degrees during physical work and the central nervous system begins to fail. It differs from classic heat stroke in that it is driven by the heat an athlete generates through exercise rather than by ambient conditions alone, and it can occur in conditions that do not appear extreme.
Can heat stroke be mistaken for a cardiac arrest?
Yes. Severe hyperthermia places extreme demand on the cardiovascular system and can itself produce a cardiac event, so an athlete who collapses after a hot session may present as cardiac regardless of what put them there. Only a core temperature reading taken at the point of collapse distinguishes the two, and it is rarely taken, which means heat is very likely under-counted in sport.
What is WBGT and why is it used instead of air temperature?
Wet bulb globe temperature combines air temperature, humidity, radiant heat and air movement into a single index. Air temperature alone ignores the three variables that determine whether an athlete can shed heat, which is why humid conditions at 30 degrees can present greater risk than dry conditions at 35.
How long does it take to acclimatise an athlete to heat?
Seven to fourteen days of progressive, controlled exposure produces the main adaptations, including earlier sweating, a higher sweat rate, plasma volume expansion and reduced cardiovascular strain. The adaptations decay within roughly two weeks once exposure stops.
Who is at highest risk of heat illness in a squad?
Athletes returning from the off-season, new arrivals from cooler climates, anyone returning from illness, athletes carrying the greatest body mass, and anyone with a history of previous heat illness, which is the strongest single predictor.
Can heat stroke happen indoors?
Yes. Poorly ventilated indoor spaces retain heat and humidity with no air movement, and a short indoor session following an outdoor one can present the higher risk of the two. Most heat policies are written around outdoor conditions and do not cover indoor training.
Does drinking enough water prevent heat stroke?
No. Hydration supports sweating and cardiovascular function and is worth managing, and it does not prevent exertional heat stroke on its own. Acclimatisation, session design and environmental measurement are the controls that determine risk.
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