uncontrollable muscle spasms are common occurrences. Once the aviator is awake, he/she will
feel weak. This impaired ability to fly may last as long as 30 minutes.
The Air Force and Navy have reported numerous Class A mishaps since identifying G-LOC as a
possible causal factor for aircraft accidents. The Air Force estimates at least 12% of all
fighter/trainer pilots have experienced G-LOC at least once. The G loading capability of the
T-6A is comparable to most fighter/trainer jets and is therefore notorious for causing G-LOC
among new pilots. Most G-LOC incidents in similar aircraft occur during G loading of 3 to 5 Gs
during rapid G loading intervals of two to five seconds.
THE ANTI-G STRAINING MANEUVER
There are two components to the recommended Anti-G Straining Maneuver (AGSM):
1. A continuous and maximum contraction (if necessary) of all skeletal muscles including the
arms, legs, chest, and abdominal muscles (and any other muscles if possible). Tensing of the
skeletal muscles reduces blood in the G dependent areas of the body and assists in retaining or
returning the blood to the thoracic (chest) area, the heart and brain.
2. The respiratory component of the AGSM is repeated at 2.5 - 3.0 second intervals. The
purpose of the respiratory component is to counter the downward G force by increasing chest
pressure by expanding the lungs. This increased pressure forces blood to flow from the heart to
The respiratory tract is an open breathing system which starts at the nose and mouth and ends
deep in the lungs. The respiratory tract can be completely closed off at several different points.
The most effective point is to close the system off at the glottis.
Closing the glottis (which is located behind the "Adam's Apple") yields the highest increase of
chest pressure. You can find it and close it off by saying the word "Hick." This should be said
following a deep inspiration and forcefully closing the glottis as you say "Hick." Bear down for
2.5 to 3.0 seconds, and then rapidly exhale by finishing the word "Hick." This is immediately
followed by the next deep inhalation repeating the cycle. The exhalation and inhalation phase
should last no more than 0.5 to 1.0 second.
1. Do not hold your respiratory straining too long (more than five
seconds) since this will prevent the proper returning of blood to the
heart and may result in loss of consciousness.
2. Anticipate a rapid-onset, high G exposure whenever possible.
The skeletal muscles should be tensed prior to the onset of Gs and
coupled with the "Hick" cycle as the increasing of G'begins.
Initiating the AGSM too early can inhibit the body's natural
cardiovascular reflex responses. Starting the AGSM too late is a
difficult situation to make up without reducing the G- stress.