The research used a helmet called the Revolution IQ HITS that uses six sensors to measure in real time the amount of g-force a player's head experiences at impact, where the hit occurs, and where it comes from. G-force is a measure of acceleration against the Earth's gravitational pull. One g is a person's weight at sea level. In car crash tests at 25 m.p.h., dummies hit windshields at 100g. Football players commonly experience hits at forces between 50g and 100g. Previous research suggested that concussions likely resulted at forces above 75g, but the new study indicates otherwise.
Between 2004 and 2006, University of North Carolina football players wore the helmets during practice sessions and games. Some players sustained concussions undergoing hits just above 60g while others had no sign of injury after a hit above 90g. Other findings showed that a single knock to the head at an impact greater than 90g does not always result in immediate concussion symptoms, such as headache, nausea, blurred vision, or ringing in the ears. In fact, location, not necessarily force, seemed to play a significant role in brain injury. Six out of 13 players that sustained a concussion had experienced impacts at the top of their head, as opposed to the side.