Before You Race: Preventing Hyperthermia, Heat Syncope and Post-Exercise Hypotension
A practical preparation guide for HYROX-style events, running races and high-intensity competitions.
Hyperthermia and hypotension are different problems, but athletes can experience symptoms that look similar: dizziness, weakness, collapse, confusion or inability to continue. The safest approach is not to guess. Prepare well, recognize red flags early and involve medical professionals quickly when symptoms are severe or unclear.
First, know the difference
| Condition | What it means | Why it matters |
| Hyperthermia / exertional heat illness | Body temperature rises beyond safe regulation during heat exposure, intense exercise or both. | Can progress to exertional heat stroke, a medical emergency involving high temperature plus brain/behavior changes. |
| Heat syncope | Fainting or dizziness linked to heat, standing, dehydration or poor acclimatization. | Often improves with rest, cooling and fluids, but must be distinguished from heat stroke or cardiac causes. |
| Exercise-associated collapse / post-exercise hypotension | A collapse after strenuous exercise, often related to blood pooling in the legs after the muscle pump stops. | Usually occurs after finishing. Collapse during exercise is more concerning and needs urgent assessment. |
| Exercise-associated hyponatremia | Low blood sodium that can happen when athletes drink too much fluid relative to losses. | Can mimic heat illness with nausea, headache, confusion or collapse, and severe cases require urgent medical care. |
Build heat readiness before race week
NATA recommends gradual heat acclimatization over 7 to 14 days when athletes will be training or competing in heat. Even for indoor events, acclimatization matters if athletes are traveling through hot weather, waiting outdoors, warming up in warm areas or arriving after a sudden regional heat spike. [7]
- Add heat exposure gradually; do not jump from cool-weather training to maximal racing in hot conditions.
- Practice race-like intensity, transitions and recovery under safe supervision before competition day.
- Use lower intensity during early heat exposure, then progress only if recovery, sleep and hydration are normal.
- Know your personal warning signs: dizziness, chills, nausea, unusual fatigue, headache, coordination problems, dark urine or feeling mentally 'off.'
Make hydration individual, not extreme
Hydration is protective, but both dehydration and overhydration can be dangerous. The ACSM position stand on exercise and fluid replacement recommends starting activity well hydrated and avoiding excessive dehydration greater than about 2% of body weight during exercise; it also emphasizes that sweat rate varies widely and that fluid plans should be individualized. [8]
For longer endurance efforts, overdrinking can contribute to exercise-associated hyponatremia. A 2017 review in Frontiers in Medicine states that drinking beyond thirst remains a primary factor in exercise-associated hyponatremia and that drinking according to thirst is an individualized prevention strategy in many exercise settings. [13]
- Do not arrive thirsty or dehydrated; drink normally with meals in the day before the event.
- Do not force large volumes of water 'just in case.' More is not always safer.
- For long or very sweaty training, estimate sweat rate by weighing before and after a similar session.
- Use electrolytes when appropriate, especially with long duration, heavy sweat or salty sweat, but do not self-prescribe salt tablets.
- If you are taking diuretics, blood-pressure medication, stimulants, antidepressants, antihistamines or other medicines that may affect hydration, blood pressure or heat tolerance, ask a clinician how to prepare safely.
Protect blood pressure before, during and after effort
Exercise-associated collapse is also known as exercise-associated postural hypotension. NCBI Bookshelf describes it as inability to stand or walk unaided during or after strenuous exercise, often related to transient orthostatic hypotension, volume depletion, peripheral vasodilation and reduced venous return. [9]
World Athletics teaches that exercise-associated collapse is a type of postural hypotension related to pooling of blood in the legs after the calf muscles stop working, and that athletes should be encouraged to keep walking through the finish area. [10]
- Avoid standing still immediately after finishing. Keep walking slowly if you are able.
- If you feel faint, sit or lie down in a cool place and tell someone immediately.
- Elevate the legs if post-exercise lightheadedness occurs and serious causes have been ruled out by medical staff.
- Eat and drink normally after the race; include fluids, carbohydrates and some sodium from food or appropriate drinks.
- Do not leave a faint or collapsed athlete alone, even if they say they are fine.
Know when fainting is not 'normal'
Post-finish lightheadedness can happen, but fainting during exercise, recurrent fainting, chest pain, palpitations, shortness of breath out of proportion, seizure-like activity, family history of sudden cardiac death, or any collapse with confusion should be treated as potentially serious. American Family Physician notes that exercise-related syncope warrants investigation and that syncope during exercise is more concerning than post-exertional events. [11]
- Seek medical evaluation before returning to intense training if you fainted, collapsed or had unexplained near-syncope.
- Do not return to competition the same day after suspected heat stroke, unexplained collapse, chest pain, seizure, loss of consciousness or confusion.
- Tell medical staff about medications, supplements, recent illness, alcohol use, previous heat illness, previous collapse and any family cardiac history.
Build a 48-hour race plan
| Time | Athlete focus | Practical actions |
| 48-24 hours before | Arrive recovered and hydrated. | Sleep, regular meals, normal fluids, avoid alcohol, check weather, reduce unnecessary sun exposure and avoid last-minute maximal training. |
| Race morning | Start fueled but not overloaded. | Eat familiar foods, drink normally, use electrolytes if part of your tested plan, avoid long waits in direct sun, and do not overdo caffeine or stimulants. |
| Warm-up | Raise readiness without overheating. | Keep warm-up purposeful and brief. Stop if you feel dizzy, nauseated, unusually weak, chilled or mentally off. |
| During competition | Pace and monitor symptoms. | Use available fluids, stay aware of dizziness/confusion/nausea, ask for help early, and do not let pride override medical warning signs. |
| Immediately after | Cool down and protect blood pressure. | Keep walking if able, move to cooler air, change out of soaked clothing if needed, sit/lie down if lightheaded, and recover with fluids and food. |
| Later that day | Watch for delayed problems. | Seek medical help for persistent vomiting, confusion, fainting, chest pain, severe headache, dark urine, extreme weakness or symptoms that return. |
Use a buddy system
The CDC recommends monitoring a teammate's condition and having someone monitor yours during heat exposure. In practice, that means agreeing before race day that either person can call for help, even if the athlete in trouble protests. [5]
- Share your start time, expected finish time and emergency contact.
- Tell your training partner if you have a history of fainting, heat illness, asthma, heart symptoms or medication-related heat sensitivity.
- Use plain language if you see danger: 'You are confused. We are getting medical help now.'
- Spectators should know where the medical tent is and how to alert event staff quickly.
Stop early for red flags
Stopping early is not failure. It is risk management. Heat stroke can progress rapidly, and hypotension or collapse can hide more serious problems. If symptoms are severe, unusual or worsening, treat the situation as medical until trained staff say otherwise.
- Stop and seek help: dizziness that does not settle, faintness, loss of coordination, repeated vomiting, confusion, slurred speech, chest pain, palpitations, severe shortness of breath, seizure, collapse or inability to walk normally.
- Cool immediately: shade, cooler air, remove excess clothing, cold towels or ice packs, water misting/fanning, or cold-water immersion if medical staff have protocols in place.
- Call emergency services if heat stroke is suspected, if consciousness changes, or if the person collapses or cannot be safely assessed.
Quick Reference
Red Flags and Immediate Actions
For athletes, coaches, volunteers and spectators at high-intensity fitness events.
| What you see | Possible concern | What to do immediately |
| Confusion, slurred speech, unusual behavior, aggression, seizure or loss of consciousness | Possible exertional heat stroke or another serious emergency | Call emergency services/event medical team. Start rapid cooling. Do not leave the person alone. |
| Collapse during exercise | More concerning than post-finish collapse; could be heat stroke, cardiac, hyponatremia or other emergency | Activate medical help immediately. Do not assume it is simple fainting. |
| Faint or dizzy after finishing, conscious and improving | Possible post-exercise hypotension / exercise-associated collapse | Move to cool place, monitor, keep lying or sitting, elevate legs if appropriate, provide fluids only if fully alert and able to swallow. |
| Nausea, headache, weakness, heavy sweating, thirst, reduced urine | Possible heat exhaustion or dehydration | Stop activity, cool down, drink small sips, seek medical evaluation if symptoms worsen or do not improve. |
| Headache, nausea, bloating, confusion after drinking a lot of fluid | Possible overhydration / exercise-associated hyponatremia | Seek medical care. Do not force more fluids until assessed. |
| Chest pain, palpitations, severe shortness of breath or fainting during exertion | Possible cardiac or respiratory emergency | Call emergency services and event medical team. Do not return to activity. |
This guide is educational and does not replace medical advice, event medical protocols or emergency services. When in doubt, treat collapse, confusion or suspected heat stroke as an emergency.
References
[1] Le Progres. Drame a l'Hyrox de Lyon : une sportive de 28 ans meurt des suites d'une hyperthermie en pleine epreuve. https://www.leprogres.fr/faits-divers-justice/2026/05/25/drame-a-l-hyrox-de-lyon-une-sportive-de-28-ans-meurt-des-suites-d-une-hyperthermie-en-pleine-epreuve
[2] TF1info / AFP. Lyon : une femme meurt apres un coup de chaud pendant une competition sportive de haute intensite. https://www.tf1info.fr/sport/lyon-hyrox-mort-d-une-femme-participante-decedee-apres-un-coup-de-chaud-hyperthermie-pendant-une-competition-sportive-de-haute-intensite-2443421.html
[3] HYROX. Creapure HYROX Lyon event page. https://hyrox.com/event/hyrox-lyon/
[4] HYROX. The Fitness Race - race format. https://hyrox.com/the-fitness-race/
[5] Centers for Disease Control and Prevention. Heat and Athletes. https://www.cdc.gov/heat-health/risk-factors/heat-and-athletes.html
[6] CDC / NIOSH. Heat-related Illnesses. https://www.cdc.gov/niosh/heat-stress/about/illnesses.html
[7] National Athletic Trainers' Association. NATA Publishes New Exertional Heat Illnesses Position Statement. https://www.nata.org/press-release/092115/nata-publishes-new-exertional-heat-illnesses-position-statement
[8] American College of Sports Medicine. Position Stand: Exercise and Fluid Replacement. https://pubmed.ncbi.nlm.nih.gov/17277604/
[9] NCBI Bookshelf / StatPearls. Exercise-Associated Collapse. https://www.ncbi.nlm.nih.gov/books/NBK576425/
[10] World Athletics - World Academy for Endurance Medicine. Module II - Exercise-Associated Collapse. https://worldathletics.org/waendurancemedicine/exercise-associated-collapse
[11] American Family Physician. Exercise-Related Syncope in the Young Athlete: Reassurance, Restriction or Referral?. https://www.aafp.org/afp/1999/1101/p2001
[12] Mayo Clinic. Heatstroke: First aid. https://www.mayoclinic.org/first-aid/first-aid-heatstroke/basics/art-20056655
[13] Frontiers in Medicine. Exercise-Associated Hyponatremia: 2017 Update. https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2017.00021/full
[14] Service-Public.fr. What are the emergency numbers (Samu, firefighters...) and listening numbers?. https://www.service-public.gouv.fr/particuliers/vosdroits/F33954?lang=en
Editorial note: This article refers only to public reporting and focuses the prevention guide on general athlete education.