Long distance? Tame the heat to perform!

You got an ironman planned this summer? Then this article could save you from some misadventures. Because if the race is run under the heat and you are not prepared for it, you might as well start to expect a delay of 30′ to 45’… being optimistic!



Over the long, the strain of heat is not cardiovascular, even if the heart beats faster and you sweat and breath more. No, the fundamental problem is nervous! The accumulation of heat causes the nervous system to be unable to activate the muscles properly: the “head” can no longer keep pace.



Our approach is based on a combination of tools aiming at a single goal: avoiding a significant increase in core and skin temperatures during the competition. Behind this, the idea will be to preserve as much as possible a “normal” physiological state. The issue, it is that each athlete has his own tolerance to heat… As a result, the event-related recommendations diverge.

Example for 2 triathletes performing their race under 35°C and having the same critical speed of 14 km.h. In temperate conditions, they would normally have a marathon pacing at 12.3±0.5 km.h.

  • Triathlete 1 that tolerates heat well: Acclimatization from D-7 | Pacing 11.5-12.0 km.h | Hydration managed to the sensation of thirst.
  • Triathlete 2 in great difficulty when it is hot : Acclimatization from D-21 | Pacing 10.3-10.8 km.h | Timed hydration at intervals of 12′ | Insulated bottles for the cycling part (to keep the drink <10°C) | Cooling strategies during the race.


These recommendations take into account that:

Thanks to acclimatisation, the pacing can be reduced by 3% rather than 8% without acclimatisation. Indeed, a successful acclimatization will bring you closer to your standard pace despite the heat. However, successful acclimatisation also requires an increase in hydration: 2 to 3 more sips per intake because sweating is increased by 10% to 30%.

Your marathon pacing is fundamentally dependent on how you have handled the heat on your bike. Fortunately, the strong convection linked to the air flow reduces the negative effects of heat. To estimate this, training of the type “bike + run” in heat will help you (eg: very strong cardiac drift with +20bpm after 60′, feeling of effort of 7/10 instead of 5/10).


One observation remains universal after all: endurance performance is never improved in a warm environment. That is to say that even if your level of performance is good (example of Jan Frodeno’s record in Frankfurt in 2015 under 38°C), it will be lower than it would have been in a temperate environment. Over long distances (half, full-ironman), heat is one of the worst constraints!



1- The “classic” method optimized.

– Hydrate yourself right before the race (1h30 before the start): 4 to 6 sips of an exercise drink diluted with water and charged with electrolytes, in intervals of 15′. During the race, also use diluted exercise drinks (2:1 ratio because you hydrate more). This will protect your gastric comfort while facilitating the assimilation of nutrients. Drink between 700ml and 1L per hour depending on your sweat rate.

– Do not start the running part at a normal pace! This may seem obvious to you but with the event context, you will tend to spontaneously reproduce your paces. Except that in heat, it will only take 10-15′ to pay for the broken pots. A speed 5% to 10% lower than normal can then be recommended (ex: 11.1-11.7 km.h instead of 12.3 km.h). Try to experience it before the race in an environment as warm as your future competition. Thirty minutes of running after a bike ride will be enough for you to get an idea.

– Promote cadence in cycling rather than the power ! A fast cadence increases the air movement around the legs and thus improves thermoregulation.

– Not all supplies should be synonymous of hydration! By over-hydrating yourself, you risk hyponatremia like stomach aches. However, the passage under the showers, the water spilled on the body and in the cap, the ice cubes in the gloves and the mouth (available on events like Hawaii)… are precious. Always use them.


2- The reference method: acclimatization to heat.

Its goal is to teach your body to better manage heat. How? By repeatedly exposing yourself to hot conditions. Why? Because your body will sweat more, because you will save carbohydrates during exercise, because your muscles will be less acid, oxygen consumption lowered…

But logistically, it’s not that easy. A bit like nutritional diets, it can be complicated to “acclimatize well” because the training conditions are not always suitable. Here are different examples of sessions, all effective:

  • If the temperature outside is >30°C: Running | Outdoor | ≥60′.

First find in your session history the average value of your HR on low intensity workouts (55-65% HP) performed at mild temperatures of 10-15°C. Then stabilize this HR during your session in heat: if you are normally at 148 bpm @12 Km/h, keep a fixed HR of 148 bpm during your first acclimatization sessions and adjust your pace over the session accordingly. Your body will start to adapt when you start running faster while keeping 148 bpm..

  • If the outside temperature is <30°C: Bicycle | Home-trainer Indoor (garage or bathroom heated to >30°C) | Without fan.

This type of session can be done in isolation (ex: 70′ @55-65% CP). But it can also be done immediately after a first outdoor training. This mode will allow to use the body temperature increase from the 1st session to shorten the duration of the Indoor part (50′ @55-65% CP).

  • If the training cannot take place in heat: Hot bath | 40°C | 40′ or Sauna | 80-100°C | 3×10′ | Without cold shower between exposures.

This type of session can also be done alone or after a training session. In the second case, the duration can be reduced to 30′ for the hot bath and 3×8′ for the sauna.


Once your sessions are scheduled, remember a few tips:

Planning: get in time! The more you suffer from heat, the earlier you should start: 3 weeks before the event rather than 10 days.

Progressiveness: wanting to go too fast by holding standard intensities on the first sessions, you will burn yourself out. At the beginning, pacing and high intensity sessions must continue to be done in cool weather (early morning or evening) to maintain quality sessions. Instead of adding intensity into heat, reduce/remove your hydration or cover yourself more to stimulate your thermolysis, this will improve your adaptations to heat.

Regularity: do not let more than 3 days pass between 2 exposures to heat. The more time passes, the more you lose the developed physiological adaptations.

Hydration: do not use cold drinks during your heat training. You like it, but this would limit your body’s rise in temperature and thus counteract your adaptation to heat. In fact, during training, we try to warm the body to teach it to cool down so that it can cool down during the race to preserve its performance capabilities.

In the end, after this type of training, 100% of the athletes are more efficient. Moreover, the benefits are also likely for events in temperate conditions.

One last thing about acclimatization. You’ll know you’re acclimatised when:

  • Your HR in heat is close to the HR you had in temperate conditions for the same intensities.
  • You stop sweating 5′ after the end of your heat session instead of 10′.
  • Your feeling of exertion decreases and the feeling of heat is less oppressive.
  • Your pacing intensities in warmth are close to your usual pace.


3- The cooling method.

Its purpose is also to avoid a significant rise in body temperature. How? By cooling the skin, stomach and/or intestines. This is called external and internal cooling. The cooling strategies are multiple: drink, crushed ice, bath, shower, fan, packs, jacket, compresses, towels… We know that the more they are combined, the more effective they are (but still less than acclimatization!).

In triathlon, it is not very useful to cool down before swimming (except if you sweat profusely and are mentally tired due to heat) because in water, the effects are null. On the other hand, on the race part (and during the bike for the most heat intolerant ones), the cold can have a positive impact on the feeling and the pace. This impact is currently estimated at 5-10% of performance, but the study tests are mainly 30′ to 60′ tests.


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