MINNEAPOLIS (AP) — A new study highlights the heightened danger to young athletes who suffer concussions and sustain new head blows before they’ve fully recovered.

The study, published Monday in Pediatrics, dug into the National Registry of Sudden Death in Young Athletes, a database maintained by the Minneapolis Heart Institute Foundation, to focus on deaths from blunt trauma among players 21 and younger. Previous studies from the data focused on deaths from cardiovascular problems.

A key finding, author Dr. Barry Maron said in an interview, was a worrisome number of prep football players who died of head and neck blows after they had already sustained concussions a few days to four weeks beforehand. Maron said it comes at a time of growing awareness about concussions, including the dangers of “second-impact syndrome.”

The registry listed 1,827 sudden deaths among young athletes from 1980-2009. Fourteen percent of them, or 261, were caused by trauma-related injuries. Trauma fatalities were most frequent in football at 148, including 17 high school players who died of head or neck injuries after they had already sustained concussions a few days to four weeks beforehand.

In general, the authors wrote, trauma deaths among young athletes are relatively uncommon, and they’re four times less common than cardiovascular deaths. The average has remained relatively constant around nine per year. “Nevertheless, these catastrophic events remain an important public health issue with a devastating effect on families, communities, and physicians,” the study said.

The study said most of the deaths were preventable and showed the importance of better equipment, better protocols for when injured athletes should return to action, and possible changes in blocking and tackling rules.

Dr. Joel Brenner, incoming chairman of the Council on Sports, Medicine and Fitness of the American Academy of Pediatrics, said the study contains important new information.

“It gives credence to everything we’ve been trying to do to make it safer for young athletes out there with proper treatment of concussions,” said Brenner, medical director of the sports medicine program at Children’s Hospital of the King’s Daughters in Norfolk, Va.

Given recent moves across the country to bar athletes with concussions from playing until they’ve fully recovered, the study also hit home for Jon Almquist, head of the athletic training program for Fairfax County Public Schools in Virginia. He said the 17 deaths were probably preventable.

“Maybe that catastrophic number can take a dip because of the changing awareness and changing concussion protocols,” said Almquist, who chairs the secondary school athletic trainers committee of the National Athletic Trainers Association.