Most Hyrox events are indoor, but indoor doesn't mean cold. A packed arena with 3,000 athletes warming up, racing, and recovering produces enough heat to push the air temperature to 24-28°C even in February. Summer events in older venues without strong air-handling can be hotter.
This guide is what to do about it.
What heat does to your race
Above 24°C, the body has to divert blood flow to the skin for cooling. That blood isn't available for the working muscles. Three measurable consequences:
- Heart rate climbs 5-15 bpm for the same effort.
- Sustained aerobic capacity drops 3-8%.
- Sweat rate rises by 30-100%, accelerating dehydration.
For a 90-minute Hyrox at 26°C, expect a 3-5 minute slower finish than the same effort at 18°C. This isn't weakness; it's physiology.
Heat acclimation: training adaptation
The body adapts to heat. The protocol:
- 2-3 weeks of regular hot-environment training.
- 10-14 sessions at moderate intensity, 45-90 minutes each.
- Add layers if your training environment isn't naturally hot. A long-sleeved top + jacket can simulate 4-6°C of additional heat.
What changes after acclimation:
- Sweat starts earlier in the session.
- Sweat is more dilute (less salt loss per litre).
- Plasma volume expands 7-12%.
- Perceived effort at the same heart rate drops.
For a race in 8 weeks, start heat training 4-5 weeks out. Acclimation peaks around week 2 and plateaus.
Race-week hydration
48 hours before race:
- Increase water intake by 500-1000 ml/day above baseline.
- Add electrolytes to one bottle per day (sodium 500-1000 mg, plus potassium and magnesium).
- Monitor urine colour. Light yellow = good. Dark = drink more. Completely clear = over-hydrated, add electrolytes.
24 hours before:
- Continue hydrated state.
- Add salt to meals. Don't go crazy; an extra 1-2 g sodium per day is plenty.
Race morning:
- 500 ml of water with electrolytes 2-3 hours before.
- 200-300 ml 30 minutes before.
- Final sip 10 minutes before start.
Pre-cooling
In the hour before the race, three pre-cooling techniques work:
- Cold water on wrists and back of neck. 60-90 seconds of cold flannel application. Drops core temperature 0.2-0.4°C.
- Cold drink. 300-500 ml of cold (not iced) water in the hour before. Internal cooling.
- Stay in the shade. Avoid baking in the sun in your warm-up gear.
What doesn't work: ice baths (constricts blood flow, can backfire), excessive caffeine (raises core temperature).
During the race
Sip water at every aid station. Don't gulp; it doesn't absorb faster and risks GI upset.
If the race is genuinely hot (28°C+):
- Drink at every aid station (most events have stations after stations 2, 4, 6).
- Pour water on the head and wrists if available. Evaporative cooling helps.
- Pace conservatively in the first 5 km. Heat compounds across the race; what feels easy at station 2 feels impossible at station 7.
What to wear in heat
Lighter than your training kit usually:
- Lightest breathable top you own. Vest tops work. Avoid cotton.
- Shorts preferred over leggings.
- Sweat-wicking sports bra for women.
- Headband to keep sweat out of eyes (more important in heat).
Skip:
- Compression garments. Trap heat. Marginal performance benefit; significant heat cost.
- Hats. Sometimes useful outdoors but inside they trap heat against the head.
- Long sleeves. Even thin ones add 1-2°C of effective body temperature.
Pacing adjustments
For a race 3-5°C hotter than your training environment, accept that your time will be 3-5 minutes slower. Pace for the conditions, not your historic PB.
The mental shift: aim for a controlled, well-executed race, not a fast race. The athletes who try to beat their cool-weather PB on a hot day are the ones who blow up at station 6.
Watch the warning signs
Heat exhaustion symptoms during a race:
- Stop sweating despite working hard.
- Goosebumps despite heat.
- Sudden dizziness or confusion.
- Muscle cramping in unusual places.
- Pale, clammy skin.
If you experience these, stop. Get to a cool area. Drink water. Find a medic.
A finishing time is not worth heat stroke. Recovery from heat exhaustion takes weeks; recovery from a slow Hyrox takes days.
Outdoor hot events
Some Hyrox events run partially outdoors (summer, Mediterranean venues). Additional considerations:
- Sunscreen. SPF 30+ on exposed skin. Sunburn during a race is a real possibility.
- Sunglasses. Useful for the runs.
- More water than indoor. Add 200-300 ml to pre-race hydration.
Training during a hot summer
If you're training through summer for an autumn race:
- Embrace the heat as acclimation. Don't only train in the cool early morning.
- Hydrate aggressively post-session. Body weight change is the guide: 1.5 L per kg lost.
- One easy day per week. Heat training adds cumulative load; you need more recovery than usual.
The honest summary
Heat is part of Hyrox. Even indoor events get warm. Train for it (heat acclimation 2-3 weeks before), hydrate for it (48 hours of deliberate fuelling), pre-cool for it (cold water + cold drinks), and pace for it (3-5 minutes slower than cool-weather target).
Don't fight the conditions. A controlled race in heat is better than a blown-up race chasing a cool-day PB. The wins come from athletes who respect what the temperature does to physiology.
The thermostat doesn't care about your training. Adjust the strategy and you still finish strong.
[ FAQ ]
Frequently asked
Do Hyrox arenas get hot?
Yes. Even in winter, a closed arena with thousands of athletes hits low-to-mid 20s Celsius. Summer events in less ventilated venues can exceed 28°C.
How does heat affect performance?
Above 24°C, sustained aerobic performance drops 3-8%. Above 30°C, it can drop 15-20%. Heart rate elevates for the same effort. Cooling capacity becomes a limiter.
Can you train for heat?
Yes. 10-14 sessions in a hot environment (or wearing extra layers) over 2-3 weeks produces measurable heat acclimation. Sweat rate increases, plasma volume expands, perceived effort drops.
What's the most important thing to do for a hot race?
Hydrate well in the 48 hours before. Pre-cool the body in the hour before (cold water on wrists, neck). Sip water at every aid station during. Don't try to set a PB on a hot day.
Written by
The Suth Performance teamCoaches and editors
The Suth Performance programming team, led by HYROX Elite 15 athlete Ben Sutherland.
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