Although they were designed largely to prevent skull fractures and brain contusions, football helmets do little to protect against hits to the side of the head that can cause traumatic injuries, according a a new study CBS News reported.

Researchers from Florida State University found that impacts that cause "rotational force" - when the head rotates on the neck because of the impact, causing the brain to rotate - are not warded off much by the football helmets, despite them being a source of protection for athletes.

"Protection against concussion and complications of brain injury is especially important for young players, including elementary and middle school, high school and college athletes, whose still-developing brains are more susceptible to the lasting effects of trauma," Frank Conidi, assistant clinical professor of neurology at Florida State University College of Medicine, said in a statement.

For the study, investigators placed sensors in a crash test dummy and conducted 330 tests to determine how well 10 popular football helmet brands protected against traumatic brain injury, CBS News reported.

The helmets tested were:  Adams a2000, Rawlings Quantum, Riddell 360, Riddell Revolution, Riddell Revolution Speed, Riddell VSR4, Schutt Air Advantage, Schutt DNA Pro+, Xenith X1 and Xenith X2, according to a press release.

They found that football helmets on average reduced the risk of traumatic brain injury by only 20 percent compared to not wearing a helmet. 

Researchers noted that of the 10 helmet brands tested, the Adams a2000 provided the best protection against concussion and the Schutt Air Advantage the worst. Overall, the Riddell 360 provided the most protection against closed head injury and the Adams a2000 the least, despite rating the best against concussion.

"Alarmingly, those that offered the least protection are among the most popular on the field," said Conidi. "Biomechanics researchers have long understood that rotational forces, not linear forces, are responsible for serious brain damage including concussion, brain injury complications and brain bleeds. Yet generations of football and other sports participants have been under the assumption that their brains are protected by their investment in headwear protection."

The findings were released Feb. 17 and will be presented at the annual meeting of the American Academy of Neurology this spring.