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Dehydration and G-Tolerance

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Regulacion por conduccion

An aerobatic pilot having excellent physical and psychic preparation can make a huge difference among athletes that compete at the highest level. The athlete's physical and mental state before starting any competition should be at optimal level; however the environmental conditions to which the pilot is subjected, for example the heat and humidity, can be a key factor in his performance, and as a result, in the quality of his flight.

The majority of international sports competitions, including engine-fueled aerobatic flight, are held during the summer season, a time when there are more hours of sunlight, and therefore, competition can occur until the wee hours of the evening.   But additionally, it is the time where temperatures are usually registered as the highest of the year, and in some countries temperatures can reach above 40 degrees Celsius. For this reason, it is not surprising that athletes and coaches of all sports disciplines are primarily concerned prior to the European and World Championships about the location of the events, since these meteorological conditions could be a limiting factor in the athlete's performance.

In aerobatic competitions, pilots can easily be in the flying field for 3 to 4 hours where shade and water are scarce, waiting for their turn at flight to arrive, having been exposed to the sun for long periods.  When it's time to fly, physical wear and tear is at its highest.  The strong acceleration that the body experiences, the powerful control deflections that pilots make, and the fact that a cabin is like a sauna, where temperatures can reach 10 degrees higher than the outside as a result of the greenhouse effect that the dome produces. Moreover, the majority of pilots wear fireproof flight suits of 2 and 3 layers. For all these reasons, it makes sense that experts compare this sport to running a marathon.

But how does the hot environment affect our body?

On the one hand, a pilot performing an aerobatic flight is undergoing physical exercise that causes his body temperature to rise some 3º C (up to 39.5-40 C), and of course, in response to cellular homeostasis (or, in order to maintain a stable and regular internal environment), this high temperature has to be controlled.

Our skin has the following mechanisms to compensate for this hyperthermia:

Radiation:

Our body is constantly radiating heat in the form of electromagnetic waves to the environment, and we radiate more the more active we are. However, this system is only effective until the average temperature meets or surpasses our body temperature (37 degrees C). After that, this no longer works.

Evaporation:

Evaporation of sweat is the second element of extreme importance. Water, at a specific heat, needs to absorb heat in order to evaporate. In this way, sweat absorbs our body heat causing us to cool down and our temperature to decrease.

There are two types of evaporation in our body. On the one hand, you have insensible perspiration, the result of radiating heat through the pores and respiratory channels (it's what dogs primarily do); and on the other hand, you have surface radiation, the by-product of sweat from physical exercise.   When this evaporates and changes from liquid to gas, it absorbs heat in the environment and reduces your temperature.

Convection:

Because hot air coming in contact with the skin is less dense, it rises, and the surrounding "cold" air will usually occupy its place.  Fans would produce this type of situation. However, if there is no fresh air to substitute for the hot air, this doesn't work.

Conduction:

It is the loss of heat by contact. When we come into contact with something that is at a lower temperature, we transfer heat to it, and if it's at a higher temperature, it transfers heat to us.

A good system of losing heat by conduction is to go for a swim, since the thermal conductivity of water is higher than that of air.

These are the mechanisms our skin normally has in order to have a lower temperature than the inside of the body, since the body, in order to lower its internal temperature produces a vasodilitation and increased blood flow causing us to become "red," but also cooling down our blood as quickly as possible.

How can hyperthermia occur with all these mechanisms?

Because these regulatory systems are not perfect and they have certain limitations...

For example, in the system of convection, we have a great ally if instead of a strong heat where we find ourselves competing, a light breeze blows. This is the case of our environment: Allowing air to enter our cabin and circulate around our body makes this regulatory system very effective during our activity. We have the advantage that with the height, the air is colder, improving that much more the convection regulation of our body.

I have seen many pilots that don't like to fly aerobatics with the air inlets open, because the air bothers them or the noise generated in the cabin is annoying. But this is possibly the most effective system that we have to regulate our temperature and prevent dehydration, since as we can see, the rest of the systems are more limited.

 This is the case of conduction. It is effective for an open water swimmer, but in our activity, this system is practically useless, since air is a bad conductor. Just soak your body or head with cold water before going to fly, like marathon runners do. This can help to increase the loss of heat from the body during the activity (in some cases, this may not be enough).

In evaporation, sweat is our ally, but relatively so....Evaporation of sweat and the consequent cooling down of our body depends largely on the humidity of the environment. In environments where the humidity is high, the evaporation of our sweat simply doesn't take place. If we combine high temperatures and almost 100% humidity, without a drop of wind, we have an explosive cocktail for our body. Under these conditions, our body will sweat between 1.5-2 liters/hour, awaiting the loss of heat via evaporation. If evaporation does not take place, these conditions create the resulting catastrophe: dehydration.

When the regulatory systems are saturated, our internal temperature rises, and dehydration occurs, producing high loss of hydrocarbons, mineral salts, and vitamins. These latter two are responsible for muscle fatigue.

How does dehydration affect our body and our G-tolerance?

In trained pilots, hyperthermia is already considered responsible for fatigue and in fact it is, but as we have seen, exercise in extremely hot environments (inside a flight cabin) and extremely humid environments will almost surely produce dehydration, which is an additional problem.

We know that our brain needs oxygen to function optimally. Blood transports oxygen, therefore anything that reduces blood flow to the brain reduces blood pressure or obstructs the transport of oxygen molecules, reducing our G-tolerance.

 Dehydration makes our blood become denser. The denser it becomes, the more difficult it is for our heart to pump it to our brain.  If a reduction in blood flow to our brain occurs, our G-tolerance is drastically reduced.

According to a study done on the centrifugal machine, high temperatures with severe dehydration can cause a reduction in G-tolerance by 40%. Heat alone reduces G-tolerance by 0.3G's. In the case of severe dehydration with 3% weight loss due to the loss fluids, the reduction in tolerance can reach higher than 50%.

Therefore, if you don't have to use the bathroom before flying in a competition, you're probably already dehydrated. Drink fluids from early morning on and frequently, but drink. Preferrably, drink fluids that contain a mix of vitamins, carbohydrates, and minerals, which are what we primarily lose during physical exercise. Avoid any kind of diuretic drink that contributes to the loss of liquid, like coffee, tea, alcohol, and caffeinated drinks. 

 
Read 2829 times Last modified on Friday, 17 January 2014 14:45
Alex Balcells

- Profesional pilot, aerobatic flight instructor and competitor. 

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