Heat Waves and Heat Stroke at Sporting Events: A Guide for Event Medical Providers

An exertional heat stroke at a trail race, a marathon, or an indoor fitness event plays out in minutes, and the medical provider is the link that decides the outcome. This guide is for the services and companies that build the medical cover on sporting events, and that now need to treat heat wave risk as a baseline input to their offer rather than a seasonal surprise.

Why event medical providers are on the front line

Three converging trends are changing the job.

Heat has become a major, recurring health risk. According to Santé publique France, the summer of 2025 was associated with more than 5,700 heat-attributable deaths in France, over 1,900 of them during heat wave episodes, with emergency department visits multiplied by 2.9 during those episodes. The warm season now stretches into September and October, when the sporting calendar stays dense.

High-intensity formats are exploding. Per SportsPro, Hyrox grew from roughly 570,000 participants in the 2024/25 season to close to 1.5 million in 2025/26, with race count rising from 74 to 105. The 2025/26 calendar passed 100 events for the first time. These races concentrate near-maximal effort into a short window, indoors, often in poorly ventilated venues.

Exertional heat stroke has a real, measurable, preventable incidence. At the Falmouth Road Race (7 miles, August), the reference study by DeMartini et al. (2015) reports 274 exertional heat stroke cases over 18 years, a mean incidence of 2.13 cases per 1,000 finishers, rising to 6.57 per 1,000 in the hottest year. The key figure for a provider: with immediate on-site cold water immersion, survival was 100%, and 93% of patients were discharged straight from the medical tent. For comparison, cardiac arrest in distance running remains rare, about 0.54 per 100,000 runners according to Kim et al., NEJM 2012. On a hot event, exertional heat stroke is the most likely life-threatening emergency, and the one the dispatch has the most leverage over.

What the provider must guarantee in its offer

The medical cover contract and the quote must make cooling capacity explicit, on the same footing as the number of responders or vehicles.

One working immersion cooling unit per advanced medical post, available on site before the start, not in logistics reserve and not in the transport vehicle.
A written protocol for exertional heat stroke management, aligned with the "Cool First, Transport Second" principle.
Core thermometry (rectal probe) at every post, the only reliable measure to confirm the diagnosis and decide when to stop cooling.
A numeric target: bring core temperature below 40 °C within 30 minutes of collapse. That is the threshold beyond which, per the Korey Stringer Institute, survival drops and lasting damage sets in.

The IOC consensus published in the British Journal of Sports Medicine (Racinais, Hosokawa et al.) explicitly asks organisers to ensure the availability of on-site immersion cooling equipment. A provider that bids without this component exposes the organiser, and takes on its own legal risk if an incident occurs.

Step 1: assess thermal risk with the organiser

The assessment is done in advance, in writing, and attached to the event file.

The WBGT index (wet bulb globe temperature) is the ACSM reference indicator. It combines dry temperature, humidity, solar radiation, and wind. Practical thresholds:

WBGT below 28 °C: moderate risk, reinforced monitoring
WBGT 28 to 31 °C: high risk, cooling chain on active standby
WBGT above 31 °C: very high risk, consider changing the format or the schedule
WBGT above 35 °C: dangerous conditions, discuss postponement or cancellation

The event profile modulates that risk: duration, expected intensity, start time, lack of shade and wind on the course, load carriage (trail packs), maximal-effort stations (obstacles, Hyrox format), number of participants exposed at the same time during the hottest hours.

Kollder's EHS Monitor computes WBGT in real time from local weather data and places the risk level against ACSM thresholds. It lets you document the decision and adjust the dispatch the day before and on race day.

Step 2: size the cooling chain

There is no universal participants-per-tub ratio, but four parameters support a defensible estimate.

Rotation capacity of one post: an exertional heat stroke takes 20 to 30 minutes of immersion and monitoring before transfer. One post therefore treats 2 to 3 patients per hour at most.
Cumulative exposure time: a 6-hour event at 30 °C generates far more cases than a 45-minute race.
Non-linear heat effect: the Falmouth 2003 example, at 6.57 cases per 1,000 finishers against a 2.13 mean, shows a heat spike can triple incidence in the same field. A dispatch calibrated for temperate weather becomes undersized as soon as the WBGT thresholds are crossed.
Course hot spots: sections with no shade or wind, low-pace climbs, the finish line, the recovery pen.

Sizing benchmark: for a 500 to 1,000 participant event in WBGT above 28 °C conditions, plan at least two working cooling posts, at the finish and at the most exposed point. Above 1,000 participants or WBGT above 31 °C, add a third mobile post on the course.

Step 3: equip every advanced medical post

Cooling component, non-negotiable:

Deployable immersion tub, whole-body immersion, water held between 1.5 °C and 15 °C
Enough water and ice to fill and replenish each tub for the duration of the event
Rectal temperature probes, at least one per post, with a compatible monitor
A dedicated stopwatch to track the 30-minute window

Triage and monitoring component:

Blood pressure cuffs, pulse oximeters, a portable monitor for severe cases
Glucometer (hypoglycaemia can mimic exertional heat stroke)
Fluids and IV access material
Survival blankets for the post-immersion phase (rebound hypothermia risk)

Step 4: train and position the teams

Equipment is only as good as the speed of recognition and immersion. Training points to fold into the team briefing:

Recognise exertional heat stroke: core temperature above 40 °C with neurological signs (confusion, aggression, disorientation, loss of consciousness) in someone exerting. Do not wait for the probe to suspect it.
Immerse without delay: the patient goes into cold water on site, before any transport. Stretchering to the ambulance without prior cooling is a loss of chance.
Active cooling: aim for a rate around 0.15 to 0.20 °C per minute. At Falmouth the mean immersion cooling rate was 0.22 °C per minute (DeMartini et al., 2015).
Exit from the bath: stop immersion when core temperature comes back below 38.8 to 39 °C, then monitor in the recovery area.
Roles: at least one team member trained in the immersion protocol per post, with a "timekeeper" role tracking the 30-minute window.

The Hyrox case: a format that concentrates risk

Hyrox stacks the aggravating factors: near-maximal effort for 60 to 90 minutes, an indoor environment that is often hot and poorly ventilated, high participant density, large crowds, and motivation that pushes athletes to ignore warning signs. The medical post has limited space, which calls for a cooling setup that is compact and deployable by a single person.

Specific recommendations for a provider assigned to this kind of event:

Immersion tub at the medical post, less than a minute from the competition floor, ready to use from the first wave's warm-up.
Reinforced monitoring at the loaded stations (sled push, sled pull, wall balls) and at the finish area, where most collapses occur.
Temperature and relative humidity logged inside the venue, not just outdoors.
A clear message to athletes and the organisation: an assisted withdrawal is not a failure.

Step 5: EMS coordination and transport

Give the EMS dispatch, at the start of the event, the GPS location of each advanced medical post and the nature of the cooling setup in place.
Standardised handover for every exertional heat stroke: time of collapse, initial core temperature, time cooling started, cooling rate, temperature at bath exit.
Do not interrupt cooling for transport until the thermal target is reached, unless vital instability forces an immediate departure.

Step 6: debrief, records, and liability

Log every case in the incident record, with times and temperatures.
Debrief the team after the event, and send the organiser a written report including the observed WBGT conditions and the resources deployed.
Keep these records: in a dispute, showing a dispatch that matched the recommendations of the learned societies (ACSM, IOC, Casa et al.) is central to the defence.

A tub built for multi-event providers

The Kollder tub folds into its Kollder Go bag (85×10×10cm, hybrid backpack and trolley) and deploys on its own, with no tools, in under 2 minutes by a single operator. That portability lets a provider cover several posts or several events on the same weekend without heavy logistics or dedicated setup staff. Request a quote at kollder.com/#contact.