It’s Getting Hot In Here! How to Prepare for a Hot Race.

Hot Race

We so often read post race reports of athletes that “fell apart” on the run, attributing their performance decline to the soaring heat or humidity. If we look at a race like the Ironman World Championships in Kona, from age group to professional athletes, even the fittest, strongest and well prepared athlete can come apart due to a poor response to heat.
Being able to arrive weeks prior to race to allow for environmental adaptations is a luxury not all of us can afford. And the question should be raised if that is an option, do you want to be conducting your key sessions and peak weeks in a new environment where you are trying to adapt to significant heat stress?

Key Concepts

Let’s first look at the physiology of heat stress and adaptation by exploring some key concepts;

1. Acclimation vs Acclimitisation.

For the purposes of this article we will be looking at acclimation, which is the process of utilising manmade interventions for heat adaptation. Acclimation can be more controlled, reducing the risk of heat illness. Acclimitisation refers to the process of adapting to natural environmental conditions by living in them. This can have a greater impact on training quality, and thus I wouldn’t choose this as my first point of call for athletes.

2. Blood volume:

The goal of training is to induce a physiological response that results in increased cardiac output, whereby the heart pumps more blood through the body per minute, with a stronger and more powerful heart muscle. This results in more oxygen being delivered to the brain, vital organs and working muscles. With greater oxygen delivered to working muscles, harmful metabolic byproducts are removed more rapidly. This increased cardiac output is a result of increased plasma volume and therefore total blood volume. With greater blood volume an athlete is able to dissipate heat more effectively, with increased sweat rate. These results can also be obtained through heat acclimation. When dehydrated we have low blood volume, and therefore your body is already experiencing an element of thermal (heat) stress. In the following recommendations I utilise an element of dehydration to our advantage for best adaptations. You see, our body is pretty clever, with low blood volume a number of hormone signals occur at the kidneys to increase total red blood cells. For the red blood cells to ‘go to work’ they need transport, in the form of water – resulting in an overall increase of blood volume.

3. Sweat:

You may not like the idea of smelly sweat, but sweat is the key to effectively managing heat while training or racing. Sweat is water, drawn from plasma in your blood transferred there by the skin as a cooling mechanism. With increased sweat, blood plasma volume decreases. If re-hydration is limited, blood plasma levels decrease, sweat rate decreases, the cooling effect is reduced and heart rate increases due to the viscosity (thickness) of your blood. And thus the proposed performance decline begins.(5)

4. Sodium & Potassium:

The other benefit to strategic dehydration is your body is signalled to start sweating earlier and learns to hold on to more sodium, by diluting your sweat. This process is important to avoid fatigue, faintness, headaches and muscle breakdown resulting from a compensatory impact with potassium. As sodium runs low, the kidneys are signalled to ‘give up’ levels of potassium to enable sodium retention.

Armed with the knowledge of how our system responds to heat stress and/or dehydration, the next step is to formulate a plan to help you arrive on the start line, as well prepared as possible to deal with high temps or humidity.

Tools for Heat Acclimation

Passive Heat Acclimation

1. Infrared sauna
The reason I recommend infrared sauna’s go well beyond being able to tolerate heat. The benefits of Infrared saunas (when compared with a traditional sauna) extend to improving immunity, metabolism, detoxification and relief from fatigue. In an infrared sauna you do not start to sweat immediately, the infrared heat goes deeper into the body, raises your core temperature, breaking down toxins and eliciting a sweat response that is more akin to exercise induced sweat response due to higher core temperatures. There is a lower level of humidity which makes it much easier to breathe and a relaxing experience. See resources for more information.

2. Steam room or sauna
Even though I view infrared saunas as a superior health benefit to standard saunas or steam rooms, they are much more readily available for athletes to use and integrate into weekly routine, especially post swim sessions at recreation centre. Traditional saunas will still help you adapt to heat stress, however the use of these saunas or steam rooms will be a greater stress on the body when compared with infrared heat, this needs be accounted for in your overall program and reflected with a decrease in intensity during a heat protocol.

3. Menthol rinse
Now, here’s an interesting one for you! If I told you to pack Lysterine in your transition bag to gargle mid-run, would you do it? If you said no, science says that you would be missing out on a significant advantage when it comes to tolerating heat, during a race or heat acclimation protocol. Recent studies have shown that a menthol mouth rinse helps reduce perception of heat, by lowering thermal sensation. This can be utilised during heat acclimation sessions in the sauna, reducing discomfort and increasing ability to stay in the sauna for ideal duration.

2. Active Heat Acclimation

1. Heat chamber
You can opt for a DIY approach, by putting your bike or a treadmill in a room with a heater that has a temperature sensor, while conducting a workout. This will have a greater impact on your overall training program and recovery, so ensure you or your coach adapt accordingly. Locally, you may also find university or performance centres specifically set up for heat chamber sessions.

2. Training later in the day
Hopefully it goes without saying, that you still need to take a sensible approach here. Putting yourself into a heat illness state is not going to provide the benefits you’re after. But if you live in a relatively cooler environment to where you will be racing, and want to train in conditions closer to your destination of warmer temps, a simple way is to train later in the day when temperatures are warmer than in the morning or evening.

3. Additional clothing
Whether training indoors or outdoors, by adding additional clothing such as gloves and a hat (when they wouldn’t normally be required) you can essentially trap heat in your body to simulate warmer conditions and raise core temperature.

4. Menthol rinse
As mentioned previously this is a great (or be-it unique) technique to reduce thermal sensation. Gargling while running would certainly take some skill, so maybe practice this one in training! The same concept can be utilised with a menthol skin rub to reduce thermal sensation on the skin, yep studies (4) have shown a positive impact on power output with this technique.

Sauna Protocol and Framework:

• During sauna sessions, avoid drinking water. Utilise water to splash your face or rinse your body as a cooling technique.
• If utilising a sauna session post training, do this within 30min of your workout completion, but do not re-hydrate. A post workout smoothie or fuel is okay, but avoid lots of fluid. A level of dehydration helps the adaptation process.
• If utilising a sauna pre training, best results will come from an infrared sauna due to it’s ability to increase core temperature. (Only necessary in cool training climates)
• After a sauna session, DO NOT take in excessive amounts of water or fluid straight away. Gradually rehydrate over the course of 2-3 hours to ensure results and effective sodium management.
• As for training, apply the principles of progressive overload. Start with small durations (10mins) of heat exposure and gradually build up (30-45min) over the 4 week period.

General Protocol Considerations and Framework:

• A combination of both passive and active heat acclimation techniques will yield best results
• You will need 5 – 14 days of consistent heat exposure for best results
• Start your heat acclimation protocol 4 weeks out from a key race and gradually introduce to your training over a 2 week period before increasing frequency and duration of passive and active heat sessions
• Loss of acclimation can occur within a 5 day period. So if you’re going to commit to a heat acclimation protocol, stay committed.
• 1 day prior to your race day, avoid major heat stress, much like training, you will want to taper down your heat acclimation sessions.
• In addition to heat acclimation, consider cooling techniques, such as menthol rise or the use of Ice slurry’s during training and racing. Warning: make sure you get a proper bottle for this. I recommend the Floe Bottle. See Resource list.
• With the goal to increase sweat rate and cooling, this does not call for the use of salt tablets. Seriously, stay away.
• Worried about cramping? Cramping is a magnesium and potassium issue, not a sodium issue. If concerned, seek consultation for a magnesium loading protocol pre race.


To know if you are conducting the protocol effectively and safely I recommend testing some daily metrics. Here are some options available to you, with varying levels of time, accuracy and cost;

1. Urinary analysis [Pee sticks].
By sampling your urine first thing in the morning and in a post training window, you can not only assess your level of hydration, but how well recovered you are, if your nutrition needs a boost or if immunity is compromised. You will want to purchase ‘pee sticks’ that measure 10 parameters, see resource list.

2. Sweat Testing (laboratory)
You can seek out a local provider or university that provides sweat testing to measure sodium, potassium, mineral and electrolyte loss during exercise. Some providers can send a home test kit, where you will need an enclosed room with a heater that can measure room temperature to have a controlled testing environment. Based on the results, a personalised hydration plan can be formulated for you to trial in training in preparation for race day. See resources list.

3. Pre and post training weigh in
Jumping on the scales pre and post training is a way to give a broad analysis of how hydrated or dehydrated you are. This approach is limited as it does not account for potential fat or muscle loss during exercise and thus it can be hard to determine is body weight difference is purely due to hydration status.

4. Heart rate variability (HRV)
Studies (3,6) have shown that dehydration can impact heart rate variability, showing a decrease in HRV in dehydrated athletes. However, HRV can also be decreased from illness, over-training, stress and poor recovery. So as a measure for general recovery and training readiness HRV is fantastic, however to measure hydration status directly would be subjective at best (5)

A note for female athletes and their coaches.

When conducting a heat acclimation protocol and race plan for female athletes there are additional factors to consider such as;
– Are they menstruating?
– At what phase of their menstrual cycle will they be in for race / heat acclimation protocol?
– Are they post menopause?
– Are they taking an oral contraceptive pill? If yes, what type? [mono, bi or tri-phasic]

Depending on the answer to these questions you will need to adapt hydration needs as different hormone levels impact absorption of key minerals and electrolytes. As a result, during the luteal phase of a menstrual cycle woman are more susceptible to dehydration due to a loss in blood plasma volume.


• The focus and goal of a heat acclimation protocol should be increased blood volume
• Heat acclimation is not only physiological, it is also psychological, exposure to heat stress and cooling methods decreases thermal sensation for overall improved performance
• Sweating is great!
• An element of dehydration can be used to your advantage
• Time to pack Lysterine in your transition bag – who knew!?
• Apply the principles of progressive overload, build up gradually
• The most successful protocol will be well planned, with training plan adjustments made to consider additional heat stress

Pee Sticks: 10SG, Reagent
Heart rate Variability app: Ithlete
Podcast: Real Food Reel: Benefits of Infrared Sauna, Episode 60.
Ice slurry bottle:
Sweat testing: Sweat Think Go Faster

1. ELY, M., CHEUVRONT, S., ROBERTS, W., & MONTAIN, S. (2007). Impact of Weather on Marathon-Running Performance. Medicine & Science In Sports & Exercise, 39(3), 487-493.
2. Montain, S., Ely, M., & Cheuvront, S. (2007). Marathon Performance in Thermally Stressing Conditions. Sports Medicine, 37(4), 320-323.
3. Oliveira, T., Ferreira, R., Mattos, R., Silva, J., & Lima, J. (2011). Influence of Water Intake on Post-Exercise Heart Rate Variability Recovery. Journal Of Exercise Physiology, 14(4). Retrieved from
4. Schlader, Z., Simmons, S., Stannard, S., & Mündel, T. (2011). The independent roles of temperature and thermal perception in the control of human thermoregulatory behavior. Physiology & Behavior, 103(2), 217-224.
5. Sims S (n.d.). Roar.
6. Stanley, J., Halliday, A., D’Auria, S., Buchheit, M., & Leicht, A. (2014). Effect of sauna-based heat acclimation on plasma volume and heart rate variability. European Journal Of Applied Physiology, 115(4), 785-794.