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Aerospace Physiology

Be a Better G-Monster: The Anti-G Straining Maneuver (AGSM)

The Anti-G Straining Maneuver (AGSM) is a technique that modern fighter pilots use to remain conscious despite being exposed to huge forces of gravity (G's).

By Rocky Jedick MD, MBA · · 7 min read

USAF Standard CSU-13B/P G-Suit
USAF Standard CSU-13B/P G-Suit

This installment will review the effect of G's on the human body, the Anti-G Straining Maneuver (AGSM) and how you as the modern fighter pilot can decrease the likelihood of being the victim of a G-LOC (G-induced loss of consciousness).

With the introduction of the new full-coverage G-suit, we expect GLOC occurrences and loss of aircraft/pilot due to G's to decrease significantly.

GLOC remains a significant threat to your life and the USAF mission. The F-16 is uniquely at risk. The combined Class A and E G-LOC mishap rate in USAF F-16 for Fiscal Years 1993-2009 is 1.32 per 100,000 flying hours.

VISUAL DEMONSTRATION OF THE UNTIMELY G-LOC

The Risk of Elevated G-Forces Reviewed:

  • Higher G's make blood heavier and displace blood to gravity dependent areas (away from your brain)
  • The brain is highly sensitive to cellular hypoxia (lack of oxygen or blood) and rapid loss of function follows, i.e. G-LOC
  • After cessation of cranium blood flow, reserve time of 4-6 seconds exists before total loss of function

Avoid maneuvers that sustain high G's for longer than 4-6 seconds. When required, the intensity of the AGSM must be maintained throughout the maneuver. Consider and combat inevitable muscular fatigue.

Your body will reflexively make adjustments in heart output and blood pressure to increase blood flow to brain, but this takes 6-9 seconds for this reflex to initiate. By this time, unconsciousness has likely occurred.

Rate of G-onset is just as important as absolute number of G's. Slower G-onset allow for increased cardiac compensation reflexes. Studies performed in the 1940's and 1950's by the U.S. DoD found that without any strain or G-suit, G-LOC occurred at an average of 5.4 G's at 1 G/sec rate and 4.5 G's at 2 G/sec rate.

EXAMPLE OF A STRONG AGSM AT SUSTAINED 9 G'S

The Anti-G Straining Maneuver (AGSM)

First developed during WWII, the AGSM increases aortic blood pressure, maintaining brain perfusion and pilot consciousness.

Well trained, effective AGSM can increase G-tolerance by approximately 3 G's

Two components:

  1. Breathing: Rapid (< 1 sec) exhalation/inspiration cycles every 3-4 seconds. This maintains oxygen content and decreases carbon dioxide in blood, while also relieving increased pressure of chest, and allowing the heart to refill with blood.
  2. Isometric Contraction: Flexion of skeletal muscles of legs and abdomen. This step increases pressure in chest and displaces blood away from these contracted muscles into the arms, chest, and brain.

The Anti-G Straining Maneuver MUST be an instinctive habit requiring no conscious thought by professional fighter pilots

A NOT SO STRONG AGSM

G-LOC Prevention:

New Technologies: The new full coverage G-suits may prevent more GLOC events than any other preventive measure. If you don't have the new G-suit, get it! Once you begin using the new G-suit, I recommend you NEVER return to the old G-suit.

  • Muscular endurance: The AGSM is intrinsically fatiguing and is an anaerobic activity. Focus on the larger muscles of gluts, quads and hamstrings.
  • NO SMOKING: Carbon monoxide diminishes your blood's oxygen-carrying capacity and G-tolerance.
  • AGSM Technique: Never hurts to continue to review, practice, and brief to what a good, effective AGSM looks like.
  • Nutrition: Ensuring that your glycogen (carbohydrate stores) are maximized should ensure that you have the available energy to delay fatigue.

REFERENCES:

  1. Natural Medicines Comprehensive Database, Consumer Edition
  2. Fundamentals of Aerospace Medicine (4 Ed.) by Jeffrey R. Davis MD MS, Robert Johnson MD MPH MBA, Jan Stepanek MD MPH, Jennifer A. Fogarty PhD