From the American Academy of Neurology Site: Testimony of: Jeffrey S. Kutcher, MD see page 5 , http://www.aan.com/globals/axon/assets/9009.pdf
University of Michigan, Department of Neurology
Director, Michigan NeuroSport
Chair, Sports Neurology Section
American Academy of Neurology
Before the United States Senate Committee on Commerce, Science, and Transportation, October 19th, 2011
Excerpt from Page 5-6 (please click the link about to read the whole document”
Helmets have an extremely important role to play in head injury prevention. Without them, the potential for bone fracture or intracranial injury would make many of our sports and recreational activities unacceptably risky. In this way, helmets are extremely effective pieces of equipment.
With the introduction of hard-shell helmets, for example, skull fractures and resulting deaths from playing football have essentially been eliminated. What helmets do not do well is significantly slow down the contents of the skull when the head is struck or moves suddenly.
Since concussions occur not as a result of the forces experienced by the skull, but by those
experienced by the brain, it is extremely unlikely that any helmet can be designed that will
prevent concussions to the same significant degree that they have been shown to prevent skull fractures.
Currently, there is no data in the published medical literature that shows any particular helmet being better than any other at preventing sports concussions. Such data is hard to collect for two main reasons: First, given the many variables that exist in the athletic population and the varied exposure to impacts, it is extremely difficult to perform a randomized, controlled, clinical trial on similar populations of athletes. Second, given that concussion is a clinical diagnosis, with no available reference standard or diagnostic test, any study of concussion is significantly limited by the ambiguity of the very clinical outcome that is being studied.
For these same reasons, there are no published data supporting the idea that other types of protective equipment, such as mouthguards or soccer headbands, prevent concussion. Moreover, in sports such as soccer, where protective headgear is the exception rather than the rule, I have seen the use of headgear result in athletes altering their playing style in the wrong direction, as their newfound sense of protection encourages more physically aggressive play.
While clinical data that speaks to concussion prevention is hard to generate, there are many extremely well performed laboratory studies that provide excellent data on the amount of force a helmet allows to get through to a model brain in a mechanical head. This does not mean that these data can be used to construct an estimate of concussion risk. Concussions do not occur at a particular force threshold. They occur across a wide range of forces and are dependent on the complex and variable physiological nature of each individual’s brain.”
The article continues and it worth reading http://www.aan.com/globals/axon/assets/9009.pdf