Philadelphia ? Researchers who looked at the impact of G-force on the head and neck say in a new study that roller coasters aren’t as dangerous as previous studies suggest.

Other researchers disputed the findings in Wednesday’s Journal of Neurotrauma and said more work needed to be done.

The University of Pennsylvania researchers who conducted the latest study looked at data from rides at three parks and developed a mathematical model calculating the effect of gravitational force.

They found that roller coasters don’t produce enough “head rotational acceleration” to cause either bleeding or swelling of the brain.

“Looking at the absolute maximum head acceleration, we found that those numbers were nowhere near known thresholds for brain injuries,” said Dr. Douglas H. Smith, a neuroscientist and co-author of the study.

Politicians and consumer advocates have long questioned the safety of roller coasters, citing more than a dozen reports of brain injuries since 1979, most of them since 1990. One elderly patient died.

On Oct. 1, New Jersey became the first state to limit the G-forces of amusement-park rides. Rep. Edward Markey, D-Mass., has proposed legislation that would subject roller coasters to federal oversight.

Smith and colleague David F. Meaney examined data from three rides with high G-forces: the Rock ‘n’ Roller Coaster at Disney-MGM Studios in Orlando, Fla.; Speed The Ride at the NASCAR Cafe in Las Vegas; and Face/Off at Paramount’s Kings Island near Cincinnati.

Amusement park visitors ride the Phantom's Revenge roller coaster at Kennywood Park in West Mifflin, Pa. A group of researchers says there is no evidence that even the fastest, tallest coasters cause brain injuries. Their findings were reported Wednesday in the Journal of Neurotrauma.

They found the coasters produced accelerations to the head that were one-ninth the force required to cause torn blood vessels in the brain and one-eighteenth the force required to cause brain swelling.

G-forces are what coaster riders feel during sudden up-and-down movements and when they are whipped around corners.

While a coaster such as Face/Off can produce a G-force of 5, simply “plopping” into an easy chair can produce a G-force of 8 to 10, the study said.

Dr. Robert J. Braksiek, an Iowa physician who co-wrote a study of roller coaster injuries in the January issue of Annals of Emergency Medicine, said the new research fails to account for injuries reported in the medical literature.

“Roller coasters do cause brain injury and that fact can’t be debated. Although rare, it does happen,” he said.

Markey said the researchers based their conclusions on the effect of coasters on “normal healthy individuals” rather than children or adults with pre-existing medical conditions.

Dr. Toshio Fukutake, co-author of a study contending that roller coasters were responsible for four cases of otherwise healthy patients developing bleeding on the brain, said there were much faster coasters than the ones in the Penn study.

“We need more research using a real human model on the bigger and faster machines,” he said via e-mail.