HighG

HighG, or high-G, is a colloquial term used to describe gravity or acceleration forces that exceed Earth's standard gravity (1 g). In aviation and spaceflight, high-G conditions occur during rapid maneuvering, combat turns, launch and reentry, and in laboratory testing with centrifuges. The magnitude of these accelerations is expressed in g, a unit relative to Earth's gravity.

Physiological effects depend on the direction and duration of the force. Sustained exposure to high g along the body's axis can reduce cerebral blood flow, causing grey-out, tunnel vision, or loss of consciousness. Tolerance varies: without protective equipment, humans generally tolerate around 4–6 g for a few seconds, with brief peak exposures up to about 9 g possible when anti-G suits and straining maneuvers are used.

Mitigation and equipment include g-suits that apply constrictive pressure to the legs and abdomen, anti-G straining maneuvers, and securely designed restraints and seating. In spaceflight, crewed spacecraft rely on pressure suits and reinforced cabins to protect occupants during high-G phases such as ascent and reentry, and to maintain safety in the event of abnormal accelerations.

Training and testing employ centrifuges to simulate high-G conditions, conditioning aircrew, and studying human tolerance. Data from high-G research informs the design of aircraft and spacecraft—seat and cockpit layouts, restraint systems, and medical countermeasures.

The term highG is informal and context-dependent, used across aviation, spaceflight, and physiology. It is not a formal physical category beyond describing accelerations greater than 1 g.