How G-Forces Impact the Human Body

Anyone familiar with human flight (or at the very least, roller coasters) knows about G-force. For those unfamiliar with the concept, the FAA has a pretty good primer on G-forces:

“Human beings are adapted to live and survive within the ever-present, accelerative force of gravity. While on earth, this is a constant, and we live and function with it from the day we are born until the day we die. As an infant learning to walk, we learn very quickly that a misstep will ultimately lead to a painful gravity-induced incident with the ground that we call “a fall.”

As we develop and start to solve problems, we learn that a cookie jar falling off the counter will accelerate all the way to floor with shattering results. Many hours of our youth are spent determining the results of gravity on spherical objects of various shapes and sizes to our advantage in competition. We became accustomed to gravity at the standard 1 “G-force.””

As objects accelerate through the air toward (or away) from the ground, gravitational forces exert resistance against human bodies, objects, and matter of all kinds. Human flight is a remarkable achievement that shares a vital concept with our first mode of transportation – walking – in that the object is to avoid violent collisions with the ground. As we accelerate faster and faster and fly higher and higher, the gravitational impact on our bodies grows greater.

The typical human body can withstand about 5 Gs, which can commonly be experienced on your average roller coaster. Military pilots and astronauts, however, undergo intensive G-force training that acclimates their bodies for 9 Gs. Any higher and g-induced loss of consciousness (G-LOC) clicks in, moving blood away from the brain and causing pilots to lose control of their aircrafts.

Types of G Forces

A 20 G training centrifuge at NASA.

A 20 G training centrifuge at NASA.

+Gx – Gravitational force exerted on a pilot’s body from chest to back during take off or sudden acceleration, pushing a pilot back into their seats.

-Gx – Force exerted from back to chest, pushing the pilot forward. This may occur during landings or forward impacts.

Gy – A lateral gravitational force that is exerted on the pilot’s shoulders, such as during a lateral roll.

+Gz – A gravitational force that is exerted on the vertical plane of the body, such as during a recovery from a dive or the pull into an inside loop.

-Gz – Force exerted vertically as pilots push into dives.

What effects do G forces have on the body?

The body’s response to increased G-forces (especially +Gz) is to increase heart rate in order to supply the brain with the proper blood flow. As acceleration occurs, the impact of G-forces grows and the results can be tragic. Eyes are especially susceptible to G-forces and some of the first signs of problems in the cockpit arise from partial or progressive loss of vision.

As arterial pressure in the eyes fall, pilots may begin to experience tunnel vision, gun barrel vision, and finally grey or blackout vision and the aforementioned GLOC. This phenomenon can be attributed to countless military and civilian aviation disasters over the last century.

How to Improve Your Performance

Pilots who undergo high-altitude or G-force training are confronted with extreme G-forces in the hopes that their bodies properly acclimate to these conditions and military personnel are often equipped with G-protective clothing to help offset the impact of G-forces, but there are other things pilots can do to improve their performance. Keeping a fit, healthy lifestyle that includes cardiovascular, resistance, and aerobic workouts on a regular basis can help improve performance mid-air, as can limiting alcohol consumption, resting properly before flight, and hydrating adequately for several days before flying is a pilot’s best bet to offset extreme G-forces.

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