Environmental temperature is something that presents a very real challenge to human physiology.
External ambient air temperatures in a single location can vary widely and, across different locations can range from extremes of -94°C (Eastern Antarctic Plateau, Antarctica) to 56.7°C (Furnace Creek Ranch, CA, USA).
Perhaps surprisingly given the above ranges, humans have a relatively narrow bandwidth of internal body temperature that we can endure without adverse effects.
‘Normal’ body temperature is generally seen as averaging 37°C, with clinical hypothermia (too cold) being anything below 35°C, and clinical hyperthermia (too hot) being anything over 40°C.
This looks on the face of it to be a complete mismatch and very surprising that we can deal with even minor fluctuations in environmental temperature. Thankfully, evolution has given us a remarkable ability to regulate our internal body temperature to stay within this narrow goldilocks zone.
In the remainder of this article, we are going to focus on the upper ends of these temperature ranges towards the ‘too hot’ end of the spectrum.
We will look first at how our body regulates and expels heat, then we will look at what happens when this stops working. Finally, we will dig into two case study examples of performance in different extreme heats and how they overcome the rising mercury.
Thermoregulation - dealing with the heat
The part of our brain responsible for thermoregulation (temperature control) is the hypothalamus, which serves the purpose of an internal thermostat by monitoring signals sent from thermoreceptor nerves that detect both heat and cold internally and in the skin.
This ‘thermostat’ is then able to affect and control the necessary actions that occur to regulate body temperature to stay within the normal range.
There are 4 main direct methods through which we can lose heat: convection, conduction, evaporation, and radiation.
Under normal, non-exercise conditions when the surrounding temperature is lower than the skin we lose heat by convection, conduction and radiation where heat is transferred to the air or objects we are in contact with (such as clothing).
When we begin to exercise, or when the surrounding air temperature rises above skin temperature, we begin to lose more heat via evaporation (namely, sweating).
When our body temperature rises, and this is detected by the hypothalamus, several things happen. Primarily, the body attempts to dissipate heat away from the core and organs by directing additional blood flow to the peripheral areas of the body and skin.
This is achieved by vasodilation (expanding) of the skin’s blood vessels. Due to the high surface area of the skin, this allows much of the excess heat to be brought closer to the skin, whereby it can then be dissipated externally through the methods of convection, conduction, radiation, and evaporation. In the cases we will see in extremely high temperatures, this will mainly involve significant sweating.
Additionally, our body reduces the backflow of blood to the core organs that do not directly need a high blood flow during exercise (eg: liver, stomach, digestive system) to prevent the continued rising of the core temperature.
When the skin’s blood vessels dilate the heat is transferred into the water and fluids that surround the cells and blood vessels. This fluid is then excreted from the body through sweat glands. Once on the skin, this fluid (sweat) evaporates and so, the heat is taken along with it.
Human’s ability to sweat so efficiently allows us to cope very well under fluctuations in external temperatures and lays a cornerstone for our ability to perform in extreme heat.
What happens when this heat dissipation stops working?
There are many reasons why this efficient process of heat dissipation might go wrong and we will see what happens when it does.
As we use sweating as a primary method of removing excess heat brought to the surface of the skin, if we stopped sweating we would overheat rapidly. Sweat is produced largely by water and fluids within our body so if we become significantly dehydrated, we will lose the ability to produce more sweat and will be unable to dissipate heat as effectively.
When someone is overheating, becomes dehydrated, and gets to the point that they are no longer sweating they’re in trouble unless they can cool down quickly via external means.
Other issues that directly influence the areas of the brain and body involved with managing and monitoring temperatures can also stop our body’s thermoregulation from running correctly.
When the thermoregulation processes go wrong or cannot cope with rising body temperature then there are a few different conditions that can develop and ultimately lead to death if left untreated.
Heat cramps:
When we sweat, we also lose a significant amount of salt and electrolytes through the fluids lost. In high heat and during physical work these fluid losses can account for 5-10 litres over a whole day, or significant amounts during a shorter period (eg: races, competitions, high activity levels in hot temperatures).
These electrolytes serve an important purpose in facilitating muscle contractions throughout our body and so when the levels drop below a certain point we can begin to experience muscle cramps. These can range from small and inconvenient to largely debilitating and very serious.
Heat collapse:
This is the most common type of heat-illness that is seen in individuals who have become dangerously overheated. When the skin’s blood vessels dilate, they draw more blood towards the skin and away from the core. To account for this, the heart’s output also increases to supply the increased demand.
However, this happens without there being a change in the total volume of blood circulating in the body.
This shift in blood flow distribution causes overall blood pressure in your body to drop, especially towards your core.
The resultant effects of this can include dizziness, vomiting, headaches, fainting/collapse, and neural symptoms (eg: slurred speech, confusion).
Left unchecked and untreated this can become life-threatening. Indirectly, many of these symptoms could also place an individual at increased risk of other injuries and complications depending on the situation.
Heat Stroke:
This represents the most serious heat illness and is potentially life-threatening. It occurs primarily when the internal body temperature exceeds 40°C for extended periods and the body is unable to effectively regulate temperature any longer.
Typically, heat stroke can occur in individuals with compromised circulation or in individuals who are physically exerting themselves in high temperatures for long durations.
The main cause of heat stroke is a failure of, or severe disturbance to, the temperature regulation in the hypothalamus. In these instances, the body reacts oppositely; the blood vessels constrict and you stop producing sweat so that your skin becomes dry and hot.
Blood pressure drops significantly and metabolic rates rapidly increase, all leading to severe symptoms of dizziness, headaches, and confusion. These can further lead to unconsciousness, coma, and eventually fatality.
If external cooling is not provided (eg: shade, cool water, ice baths etc) then body temperature will continue to rise unchecked.
Dealing with the heat: Extreme Real-World Examples
Case Study 1: F1 Singapore Grand Prix (Hot, humid)
The details of the race:
* 61 Laps of a street circuit
* Races here have never taken less than 1 hour 51 minutes, it is, therefore, one of the longest races on the competition calendar.
* 23 corners per lap
* The most of any track in the competition calendar. This exerts a huge physical demand on the driver’s bodies.
* Singapore's environmental conditions during the race: Around 30°C, and 80% humidity.
* Coupled with all of the very hot mechanical components in the car, this causes the temperature of the car’s cockpit to sit around 50-60°C (only slightly cooler than a typical sauna).
What does this mean for the drivers?
Well, it doesn’t take much imagination to understand how challenging it must be to manage body temperature in 60°C heat, with 80% humidity whilst wearing multiple layers of flame-proof clothing, in a car with components reaching hundreds of degrees.
This, along with the extraordinary demands of a 2-hour race with around 25% of each lap spent braking, causes exhausting muscular and cardiovascular demands.
Water loss, from sweat, during the race can be up to 3 litres (3kg) which exacerbates the potential for heat illnesses to occur.
Physically then, this is likely the most demanding race in the competition season.
Why do these race conditions make it so difficult to manage body temperature?
In high humidity, with multiple layers of clothing in a high-heat environment, sweat is unable to effectively evaporate from the skin. The ambient temperature is also so high that little heat can be lost through any of the other methods we have discussed previously.
Any drinking water that is onboard the car for the drivers would also become heated quickly and thus would not serve many benefits in internally cooling their bodies.
The 3L of water loss throughout the race means that large volumes of water must be taken on to maintain the fluid balance in the body and aid in any way possible to heat regulation.
Through all of these factors, heat regulation during the race is very difficult and in reality, little can be done to significantly cool body temperature during the race.
What methods do the teams implement to combat rising internal body temperatures during the race?
There are a few key methods implemented to aid cooling of the drivers, these can be separated into factors used during the race and those done outside of the race.
During the race, there are a few key things that are done to help regulate the driver’s temperature.
Firstly, the driver’s clothing and helmets are designed to be as lightweight as possible within the safety regulations of the race. This helps to reduce the heating effect that bulkier and heavier materials have had in the past.
Secondly, the driver’s helmet includes specific ventilation holes that allow passing air to circulate around the driver’s head during the race. Air that is cooler as the car passes through can help to decrease the heat of the driver’s head slightly.
Before the race, both in the season leading into the race and immediately before the race, there are a few ways they can help prepare the driver for the heat-stress demands.
Physical training and acclimatisation to high-heat environments before the race can help to combat some of the overheating problems that could occur. Greater cardiovascular fitness helps to manage the shifts in circulation that occur to dissipate heat more effectively, so adequately preparing ahead of the race will put the drivers in a stronger position to manage body temperatures.
Additionally, acclimatisation to high-heat environments before racing can go a long way to helping the drivers cope with the heat. This can be done either in the car during normal practice sessions or in specially built environmental chambers that can artificially create high temperature and humidity conditions. Either using this passively, similar to a sauna or by exercising within them the driver can improve their ability to dissipate heat more effectively.
Immediately before the race, pre-cooling of the driver’s body can be used. This involves the use of ice-cooled vests or ice baths. The idea is to cool their body temperature to lower than normal so that they might be able to maintain that lower temperature for longer before it raises significantly. Unfortunately, this is only a short-term fix and will not go a long way to helping hours into a race.
In effect, drivers are fighting a losing battle during this race with rising body temperatures and often finish severely exhausted and near-overheated.
The methods above can go a way to helping but ultimately, this race represents an extreme physiological challenge for the drivers.
Here are a few additional resources on the physical demands of the F1 Singapore Grand Prix:
* FIGHT NIGHT: How brutal Singapore GP pushes drivers to the limit
* The human element – why the Singapore GP represents the biggest physical test of the season
* How Hot Is An F1 Cockpit?
* The physical challenge behind F1 drivers' 'love-hate' relationship with the Singapore GP
Case study 2: Marathon des Sables (Hot, dry)
The details of the event:
* Self-proclaimed ‘Toughest Footrace on Earth’.
* Nearly half the participants drop out of the race each year, and 3 people have died during the race in its time running.
* A 6-day, multistage ultra-marathon event covering 251 km/156 miles over the Sahara Desert.
* Works out to about 6 regular marathons in total, with the longest day being around 80-90km long.
* Endless sand, steep dunes, and temperatures up to 50°C
* The Sahara desert has very high ambient temperatures during the day, made worse by very low humidity, and radiation of heat from the sand.
* All kit needs to be carried including food, water, a sleeping bag, and safety kit.
* Weighing in at around 10kg total.
What does this mean for the runners?
Aside from the extreme physical demands of running the distance in challenging under-foot conditioning over 6-days…
There is a high risk of heat illness occurring, with ambient temperatures topping out at 50°C added to high physical outputs. All whilst carrying a pack that increases the physical demand and body heat further.
As we have seen earlier on, sweating is a primary method of cooling down and during the race, you will potentially sweat up to 2-3 litres of fluid an hour. Dehydration and the implications that can have on heat regulation are a real risk during the race because of the fluid loss.
How do runners prepare for the heat before the race?
Heat acclimatisation is an area of physical preparation that can be vitally important in preparation for this race.
Aside from running training to be able to cope with the distance and running demands, specific heat acclimatisation training can be the final element that brings a competitor’s training to a peak before the race.
It is well researched that acclimating to the heat can help to increase sweating rates, you begin to sweat earlier on, lower body temperatures, and heart rate will decrease.
All these factors contribute to more efficient and effective heat regulation for the same level of physical exertion and help to combat the temperature conditions during the Marathon des Sables.
Specific methods of acclimating to heat can be done in a few ways.
If a runner lives in an area that already has high environmental temperatures, then conducting their training runs in the heat will likely be sufficient to bring about the above heat regulation adaptations.
For most people living in relatively colder climates, this is unlikely to be as feasible.
Similarly to how the F1 drivers can use specially built environmental chambers, so can runners.
This could be as simple as using a sauna before or after training or even potentially conducting some light exercise during a sauna session. Doing this allows you to extend out the time spent in high-heat environments, but in an easily controlled way that can be progressively overloaded through a training program.
Doing so before or after training allows you to raise your overall body temperature for longer. Doing so, combined with light exercise (it would be highly unrecommended to do any heavy physical exertion in a sauna) could help an individual to gain first-hand experience of exercising in hot environments before the race begins.
On the other end, specially built (very expensive and high tech) environmental chambers can be used. These are typically owned and operated by researchers or elite-level sporting organisations (such as F1 teams) so can often be hard to locate or access. But if you can, they would represent the best way to conduct heat acclimatisation training, outside of training in the Sahara itself.
Conducting steadily progressed training sessions within these chambers, building up to the types of conditions you are likely to experience during the race, would be an ideal way to prepare yourself.
What can runners do during the race to keep cooler?
In the first instance, ensuring that lightweight clothing and full-coverage hats are worn will go some way toward mitigating overheating risks.
However, the primary method of heat regulation during the race would be hydration. As previously mentioned, water loss could be anywhere from 2-3 litres (2-3 kg) per hour in the racing conditions. The issue is that our ability to absorb water is lower than our water loss. So runners need to take on significant amounts of water still with the understanding that becoming slightly dehydrated is almost inevitable.
Taking on sufficient water and electrolytes/salts during the race will allow a runner to maintain a relatively consistent sweat output and thus, regulate their heat through evaporative cooling.
Interestingly, in most cases any more than a 2% loss in body weight through dehydration would begin to affect physical and cognitive performance. But in marathon and ultra-endurance events, athletes have been seen to continue the ability to perform at as much as 4-6% dehydration.
Sufficient hydration strategies are a largely individual endeavour and so it would be best advised that runners establish what works best for them in their training leading up to the race, ideally under conditions that simulate the environmental and fluid loss demands of the actual race.
Generally, it would be advised to hydrate sufficiently before the race begins, maintain as much as is feasible during the race, and then sufficiently rehydrate after each racing day. Doing so will allow for adequate fluid balances to keep a consistent sweat rate and regulate body temperature accordingly.
Here are a few additional resources on the Marathon des Sables and how runners can prepare/cope with the heat demands:
* Marathon des Sables Website
* Marathon des Sables: how we rapidly acclimatised five runners for the gruelling race
* How Runners can Acclimate to Heat
* How to stay hydrated during the Marathon Des Sables
* Exercise in the heat - Dr Becky Neal
Closing thoughts:
Thank you for reading this article, hopefully, you found it interesting and were able to take something away from how heat can affect our bodies, and how those operating at the extreme ends of high-heat performance can cope with this.
If you had any questions, wanted to know more, or if you wanted to ask anything else please reach out via the links below:
* Email: [email protected]
* Instagram: @Apexdeltacoaching
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