Can Increased Gravitational Force Knock You Unconscious?

Space travel has fascinated us since the first time man stepped foot on Moon. However, being an astronaut is not as easy as one may think after watching those dream-like walks over the surfaces of unknown celestial bodies. To actually get into space, you have to go through a lot!

In the long list of things and experiences you have to go through before they launch you into orbit, one that is widely popularized in the media, and is somewhat dreaded by astronauts, is GLOC.

What is ‘g’?

The force of gravity all over the earth is assumed to be uniform, but in practice, it’s actually not. This is because Earth is not a perfect sphere, as almost every scientific experiment assumes, and also, its density is not constant throughout the planet.

Coming back to ‘g’, this variable is nothing but the acceleration due to gravity, often expressed in terms of g’s for simplicity. 1 g is equivalent to 9.8 meters per second squared, which, if expressed in a different set of units, is equivalent to 9.8 Newtons (of force) per kilogram of mass.

Ways that G-Forces Can Affect You

Living on the surface of Earth, everyone experiences a comfortable g-force, or in other words, a constant force of gravity that we are used to. However, unnatural g-forces can affect people, and in some cases, quite severely. There are a number of conditions that are associated with being exposed to increased g-forces, some of which include greyouts, blackouts and tunnel vision.

greyout meme

A greyout refers to the loss of color vision due to exposure to increased g-forces. Tunnel vision is quite intuitive, i.e., it refers to a condition where the subject loses their peripheral vision and is restricted only to center-facing vision. During a blackout, a subject completely loses their vision.

Loss of peripheral vision (Image Source:

Loss of peripheral vision (Image Source:

Enter G-LOC

Gravity-induced Loss Of Consciousness, often abbreviated as G-LOC, is a temporary loss of consciousness due to increased g-forces that are sustained for some time.

Image Credit: Wikipedia

Image Credit: Wikipedia

It is usually experienced by fighter pilots maneuvering through high-performance flights and astronauts during space flights, but it can also affect people on amusement park rides that are influenced by the g-forces acting on a body due to their extreme climbs, falls, twists and turns.

What Happens During G-LOC?

As stated earlier, increased and sustained g-forces cause G-LOC. Due to excessive g-forces, blood starts to drain away from the head, resulting in a condition called cerebral hypoxia. As the retina (in the eyes) are highly sensitive to hypoxia, the initial symptoms of G-LOC are usually visual. As retinal blood pressure alleviates, blood discontinues its flow towards the retina, first impacting peripheral vision, and then center-facing vision. This is the reason pilots consider the ‘loss of peripheral vision’ as an indicator/marker of their maximum performance before losing consciousness.

Image Credit: Ferenc Szelepcsenyi/Shutterstock

Image Credit: Ferenc Szelepcsenyi/Shutterstock

Similarly, astronauts experience G-LOC during lift-off when g-forces increase rapidly as the space shuttle escapes the surface of Earth. This phenomenon has been portrayed countless times in popular culture; the latest reference to this phenomenon was shown in the movie The Martian, when Mark Wattney (portrayed by Matt Damon) falls unconscious as his spaceship leaves the atmosphere of Mars.

How Can This Be Corrected or Avoided?

There are a number of factors, including age, level of training and overall fitness, that affect the threshold at which one goes unconscious, but there is no escaping G-LOC, or at least some initial symptoms, if you have signed up for a ‘g-altering’ ride. As G-LOC is experienced due to a change in g-forces (a staple of high-performance flights), there is no preventive measure to avoid that brief period of unconsciousness. Simply returning to normal conditions, or in other words, removing the conditions that caused the increased g-forces, can bring a person back to his or her senses.

Astronauts during launch (Image source:

Astronauts during launch (Image source:

Astronauts often report a brief bout of unconsciousness, which does not last more than a minute or two, after which they regain consciousness. Diverse feelings and experiences have been reported, including highly vivid dreams, during bouts of G-LOC. It takes a few minutes before the person feels normal again after regaining consciousness.

If you ever find yourself in a condition where you are about to experience G-LOC, make sure that there are people around you, and more importantly, that they like you enough to make sure you don’t collapse and crack your head open!


  1. Wikipedia
  3. Science In The News SITN
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About the Author:

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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