OUTER soft-shell layers, spray treatments, helmet pads and fiber sheets are not enough to lower the risk of getting a concussion, according to US researchers.

"Our study suggests that despite many products targeted at reducing concussions in players, there is no magic concussion prevention product on the market at this time," says study author John Lloyd, PhD, of BRAINS, Inc. in San Antonio, Fla., and a member of the American Academy of Neurology.

In the study, Dr. Lloyd and his team made adjustments to the standard drop test system that safety equipment traditionally undergoes before being approved for sale in the US.

Using a crash test dummy head and neck enabled them to get a better idea of the consequences of impact to that area of the human body, according to the study.

They placed sensors in the dummy's head to measure linear and angular rotational responses when the helmets hit the ground at speeds of 10, 12 and 14 miles per hour.

Dr. Lloyd and his team assessed four add-ons to American football helmets including Guardian Cap, UnEqual Technologies Concussion Reduction Technology (UTCRT), Shockstrips and Helmet Glide.

The four add-ons were tested five times each on both the Riddell Revolution Speed helmet and the Xenith X1 helmet.

Add-ons and all, the helmets were dropped from heights of 1.0, 1.5 and 2.0 meters and sensors recorded linear acceleration, angular velocity and angular accelerations of the false head as they hit the ground.

Compared to the helmets without the add-ons, linear accelerations were reduced by 11 percent when helmets were fitted with the GuardianCap, UTCRT and Shockstrips.

However, angular accelerations -- believed to be the major force behind a concussion-causing impact -- only subsided by two percent.

Helmet Glide made no difference when tested against a naked helmet.

The study will be presented at the American Academy of Neurology's 67th Annual Meeting in Washington, DC to be held April 18- 25.