In Do Helmets Prevent Concussion? biomechanics expert witness John D. Lloyd, Ph.D., M.Erg.S., CPE, CBIS, writes:
Concussion, also known as mild traumatic brain injury (mTBI), is a leading health issue resulting from head impacts associated with sports, recreation and transportation. Youths are particularly susceptible to head injury, though it can also devastate a professional career. Full recovery from mTBI often takes longer than expected, without which a second, even relatively innocuous, impact could have catastrophic outcomes.
Helmet manufacturers realize that their products may not reduce the risk of concussion and even NOCSAE (National Operating Committee on Standards for Athletic Equipment) standards are based on tests that ignore risks associated with concussions. Yet, clinicians recognize that brain injuries are caused by a combination of impact and impulse mechanisms, which engineers are readily able to measure in terms of linear and angular head motions.