Heat is the thing most likely to actually hurt you in Gurugram, and the single most useful fact about heat stroke is counter-intuitive: the warning sign is the brain, not the skin. Confusion, staggering or aggression in the heat is exertional heat stroke until proven otherwise — and in exertional heat stroke the skin is usually still hot and sweaty. Waiting for dry skin wastes the time that matters.
How do you recognise heat stroke?
Heat exhaustion and heat stroke sit on a spectrum, and what separates them is central nervous system involvement.
Heat exhaustion — heavy sweating, weakness, dizziness, nausea, headache, fast pulse. The person is lucid. Stop, get into shade, cool them, give fluid, and do not let them go back out.
Heat stroke — any of the above plus altered mental status: confusion, disorientation, slurred or nonsensical speech, staggering, unusual aggression, or collapse. This is a medical emergency with a real mortality rate.
What to do: cool first, transport second
This ordering is the part people get wrong, and it is the part that determines outcome. Survival in exertional heat stroke tracks how quickly core temperature comes down, not how quickly an ambulance arrives.
- Call 108 or 112 — have someone else do this while cooling starts.
- Get them into shade and get the clothing off.
- Cool aggressively, and the method matters enormously. These are not interchangeable. Cold water immersion is the validated method, cooling at around 0.22°C per minute. Improvising a tub or a tarp held as a basin is worth the effort. Failing that, iced towels rotated constantly manage roughly 0.12 to 0.16°C per minute. Ice packs to the neck, armpits and groin are an adjunct, not a method — measured at about 0.04°C per minute, roughly a fifth as fast as immersion. Do not settle for them if anything better is possible.
- Cool until they are down, then stop. Cool to about 38.6–38.9°C and then stop, because continuing past that causes hypothermia. Without a thermometer, roughly 10 to 15 minutes of immersion, and stop if they start shivering or become lucid. The target is to bring core temperature below 38.9°C within 30 minutes of collapse.
One thing that will mislead you: do not use an ear or forehead thermometer to rule this out. Oral, armpit, ear and temporal readings are all invalid in a runner who may have heat stroke, and they read falsely low — so the device will tell you it is fine when it is not. Rectal temperature is the only valid field measurement. If you do not have one, treat on mental status and cool.
For scale on why this works: at the Falmouth Road Race, 274 consecutive cases of exertional heat stroke were treated with on-site cold water immersion over 18 years, at a mean starting rectal temperature of 41.4°C. Every one of them survived — a 100% survival rate. That is the argument for cooling before transport, and it is about as clear as evidence in this field gets.
What not to do: do not make them walk it off, do not wait to see if it passes, do not give a confused person fluids to drink, and do not delay cooling in order to move them.
Does heat acclimatisation actually work?
This is the good news, and it is one of the better-evidenced adaptations in exercise physiology. Repeated exercise in heat produces real physiological change, fast:
- Plasma volume expands early, within roughly the first week of exercise-heat exposure — reported expansions in the review literature are commonly in the region of 9 to 13%, with a falling heart rate at the same workload.
- Broader adaptation takes 10 to 14 days of exercising in the heat at meaningful intensity, though seven-day protocols already show reduced cardiovascular strain and lower core temperature.
- You start sweating earlier, sweat more, and lose less sodium in it.
Practically: if you know you are racing in heat, do not avoid the heat entirely in training. Build exposure deliberately over a couple of weeks, at reduced intensity, and accept that the first sessions will feel awful. Adaptation decays at roughly 2.3% per day for the heart-rate adaptation and 2.6% per day for the core-temperature one — near enough the same rate, so do not expect one to outlast the other. Two weeks away costs you around a third of it, and returning fully to baseline takes something closer to five to seven weeks.
Running through a Gurugram summer
- Go early, and accept that this collides with the pollution peak. NCR air quality has a morning peak roughly 8 to 10am. In peak summer heat is the greater risk; in winter, air is. See our AQI guidance.
- Humidity matters as much as temperature. Sweat cools you only when it evaporates; sweat that drips off you does nothing. This is why heat-stress indices used in sport weight humidity heavily rather than going by the thermometer, and why a humid morning can be harder than a hotter dry one. Judge by how you are coping, not by the temperature reading.
- Slow down and stop watching pace. Effort at a given pace rises steeply in heat. Run by feel or by the talk test.
- Learn your sweat rate. Weigh yourself before and after a long run occasionally. Never finish heavier than you started — see how to drink on a long run.
- Run with people. The person who spots that you have stopped making sense will not be you. That is the honest argument for the group run in May.
Some people should be considerably more cautious in heat: anyone with a heart condition, on medication affecting heart rate, circulation or sweating, older runners, and anyone unwell or recently ill. See who should not run, and when to rest.
References
Casa DJ, DeMartini JK, Bergeron MF, et al. National Athletic Trainers’ Association position statement: exertional heat illnesses. J Athl Train, 2015;50(9):986–1000. · DeMartini JK, Casa DJ, Stearns R, et al. Effectiveness of cold water immersion in the treatment of exertional heat stroke at the Falmouth Road Race. Med Sci Sports Exerc, 2015;47(2):240–5. · Périard JD, Racinais S, Sawka MN. Adaptations and mechanisms of human heat acclimation: applications for competitive athletes and sports. Scand J Med Sci Sports, 2015;25(Suppl 1):20–38. · Daanen HAM, Racinais S, Périard JD. Heat acclimation decay and re-induction: a systematic review and meta-analysis. Sports Med, 2018;48(2):409–30. · Belval LN, Casa DJ, Adams WM, et al. Consensus statement: prehospital care of exertional heat stroke. Prehosp Emerg Care, 2018;22(3):392–7.