In Do Helmets Prevent Concussion? biomechanics expert witness John D. Lloyd, Ph.D., M.Erg.S., CPE, CBIS, writes:
Using proprietary miniature sensors to measure concussion risk at the center of the brain, BRAINS researchers completed more than 330 tests across ten popular helmet brands. The team concluded that while these helmets provide excellent protection from linear impacts – those leading to bruising and skull fracture – they offer little or no protection against angular acceleration, a dangerous source of brain injury and encephalopathy.
Results show percent reduction in linear impact acceleration, Head Injury Criterion (HIC), and angular acceleration provided by the different football helmets, compared to the same impact with no helmet. Note that all helmets provide considerable protection from skull fracture (blue) and focal brain impact (green), but are far less effective at reducing risk of diffuse brain injury and concussion and encephalopathy (red). In fact, some helmet designs offer no significant protection from concussion – and those that offer the least protection are among the most popular on the field.