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Sunday, 26 May 2013 00:00

Prevention of the G-LOC Part 2/2 Featured

Written by  Snap&Roll/Dr. Reguant
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Maniobra Anti-G M-1

How To Prevent G-LOC

A proven way to prevent G-LOC is undoubtedly "not pulling G's," however if you are reading this, it is likely because you've already gone beyond straight and level flight.

Simply by reading this article, you've already taken a step in preventing G-LOC, since you are increasing your understanding of the problem. If you are conscious of the possibility of G-LOC in flight, you will be capable of preventing its consequences. 


It's obvious that the best way to reduce the risk of G-LOC is to expose your body to G-level accelerations so that you can adapt. The human body has a certain "aptitude" for adapting to its surroundings and environment, Gs being no exception. A physically prepared pilot who has not flown aerobatics for a month can be back to the highest level of readiness (that is, with respect to G-tolerance) with 4 flights of adaptation.

As with all aspects of aviation, overall health plays an important roll in Gz tolerance. Colds, gastric problems, or fatigue significantly reduce your tolerance. Coffee and alcohol also affect tolerance.

Although it may not seem like it, a determining factor in increasing resistance to Gs is the angle of the plane's seatback. Keeping in mind that the distance from the heart to the brain is some 30 cm, the more the seat is reclined, the less this distance becomes, making it easier for the heart to pump blood to the brain. Increasing the incline to 80 degrees easily allows for a 15 Gz tolerance, but unfortunately this is not at all practical, since it greatly reduces horizontal as well as vertical visibility.

Anti-G suits are known throughout the military world, and they increase tolerance by 1.5-2 Gz.  Anti-G suits are basically overalls filled with balloons. When Gz forces are activated, a valve activates some pumps that fill the balloons with air.  The pressure of the balloons causes the legs and abdomen to contract, reducing the amount of blood being forced to the legs from the brain, allowing for a significant increase in tolerance.

Utilizing a similar mechanism as the anti-G suit, tightening the lower abdominal harness may increase protection from Gs, though this is not proven.

Aside from the passive methods we have described (incline, anti-G suits, etc.), the only method by which aerobatics pilots can purposely improve their tolerance for G-forces and prevent G-LOC is by breathing correctly, with simultaneous muscle contractions of the upper, lower, and abdominal extremities. These techniques are described below:

-        M-1 Muscle Contraction Maneuver:

Consists in a deep inhalation, followed immediately by a strong exhalation - partially closing the glottis for 3-5 seconds -  after which a deep inhalation is repeated in order to prevent a pressure drop in the arteries of the brain.   Simultaneously, contract the muscles of the arms and forearms, the abdomen, and the lower extremities to redirect the blood in these areas to the highest parts of the body, like the brain and the eyes.

-        L-1 Muscle Contraction Maneuver:

This technique is the most commonly used by aerobatics pilots. It is basically like the former, the difference being that the glottis remains totally closed during the course of the forced exhalations, preventing the strong groan produced with the M-1.

In both manuevers, the muscle stress is very intense and produces significant fatigue.

In the following picture, we can see the result of these maneuvers in relation to the arterial pressure of the eye.Efecto de la contracción muscular sobre la presión arterial del ojo

In regards to these maneuvers, Dr. Reguant tells us: "Having good physical conditioning is vital for doing these maneuvers and increases the aerobatic pilot's overall muscular power through anaerobic exercise (which facilitates one's muscular capacity to redistribute the blood volume from the lower extremities to the brain, while protecting the spinal column from significant stress) and aerobic exercise (which improves the cardio-respiratory capacity, facilitating the elimination of waste products and reducing muscular fatigability)."


To counteract and better tolerate the effects of Gs and prevent G-LOC during our aerobatic flight, we have to prepare ourselves physically to increase our anaerobic capacity and develop those muscle groups that are going to intervene.

It is proven that duration and tolerance to high Gs can be increased by up to 53% through an aggressive and appropriate anaerobic training program for the muscle groups that will be affected:

-        Upper Extremities

-        Lower Extremities

-        Abdominal Muscles

-        Back Muscles

The accumulation of blood in the legs and abdominal muscles can be reduced with good neuromuscular coordination of the muscles of the legs, abdominals, and back, and a good breathing technique.

The muscles involved should be sufficiently strong so that contractions can be done without using the maximum strength of these muscles. At the same time, they must have sufficient aerobic and anaerobic capacity so that these contractions can be developed over a long period of time. This requires a good cardio-respiratory system.

Lastly, you have to be careful to avoid high +Gz after -Gz. Tolerance may have been reduced significantly as explained above. This can occur in any sequence, especially because of the unknown nature of competition, where the body's physical resistance to these variations is usually put to the test.

As we have seen, the pilot's physical resistance is a determining factor in prevention. Without optimum muscular resistence the body gets tired and fatigued during the performance of maneuvers in an aerobatics sequences, making it more difficult to concentrate and causing our body to respond promptly to the actions that our brain indicates. This undoubtedly brings us closer to the G-LOC threshold.

A good free program design keeps these elements in mind, as is reflected in the majority of free programs of high-level competition pilots. Besides incorporating figures to compensate for cross-wind, height, etc., these pilots have a tendency to design programs which make the first figures more complex and with more "K" than the latter figures of the program, specifically to avoid the loss of precision caused by muscular fatigue and to avoid any possible consequence of Gs and G-LOC.

 Who can get it?

Very simple! Anyone who pulls Gs can suffer from G-LOC. Whoever enters into a G-LOC loses control of his plane. Whoever loses control of the plane can crash. Whoever crashes,....you can imagine!

We are not immune! No one is too good or too experienced to NOT suffer from G-LOC!  Even limitless pilots who have been competing at the highest level for years are NOT immune to G-LOC.

Gs are elevated for only a short duration during a typical aerobatics program, and although this may give us a certain protection, it never gives us immunity.


-        The loss of consciousness because of Gz can and does occur in a piston engine plane. G-LOC can happen to any of us if we are not careful, especially pilots of advanced capability aircraft performing aerobatic flight.

-        The fact of the matter is that loss of consciousness can occur without prior notice (grey-out, black-out) if you rapidly exceed your threshold for tolerance.

-        The memory loss that normally accompanies G-LOC leaves the pilot completely unaware that he has been unconscious and can make him incorrectly believe that he is easily able to tolerate Gz.

-        Being aware of G-LOC is probably the most significant factor in its prevention. Good health, being fit, experience, and a good practice of muscular contraction maneuvers always increases the pilot's tolerance of Gz.

-        In Spain, according to a social network survey done by Snap&Roll of our website's followers and users, 40% surveyed know the meaning of G-LOC and its consequences, but a high 33% had never heard of it. 23% had heard of it, and 4% don't know what it is, but are familiar with the term.

Thus far, no online research corroborated by medical professionals has been published in Spain about G-LOC and its consequences.  With data in hand and knowing that 37% of those surveyed are completely unfamiliar with G-LOC, the Snap&Roll team have confirmation of the importance of this article in raising awareness about this phenomenon, its effect, and its consequences - a reality from which aerobatic pilots are NEVER exempt.


Read 2982 times Last modified on Friday, 17 January 2014 14:44
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