Maxed out: How many gs can you pull?
By Clare Wilson The swooping, sickening sensations you experience on a roller coaster come courtesy of brief g-forces of up to 5 g. Rides have to be designed so people don’t black out. Our tolerance of g-forces depends not only on the magnitude and duration of the acceleration or deceleration but also on the orientation of our body. We are most vulnerable to a force acting towards the feet, because this sends blood away from the brain. Five to 10 seconds at 4 to 5 g vertically typically leads to tunnel vision and then loss of consciousness. Fighter jets can pull up to 9 g vertically, and the more a pilot can take without blacking out, the better their chances in a dogfight. Some pilots wear “g-suits” which help push the blood away from their legs and towards the brain. People with the highest g tolerance are known as “g-monsters”. “We have had people who have been perfectly conscious at 6 g,” says physiologist Alec Stevenson of UK-based defence firm Qinetiq. Others pass out at 3 g, he says. Pilots can boost their natural g tolerance by training inside centrifuges, like the one Qinetiq has in Farnborough in Hampshire. They learn to tense their leg and abdominal muscles to push blood to the upper body, and to breathe in a special way, straining hard as if defecating when constipated, to raise blood pressure. The greatest vertical force anyone has withstood is 31.25 g, although for that the subject,