Force of hit isn't big impact

The hardest blows to the head in football are not necessarily the ones that cause concussions, according to a study released Friday by the University of North Carolina.

In fact, after analyzing more than 100,000 hits, a study by UNC shows those attention-getting big hits are no more likely to cause a concussion than a routine collision.

Concussions resulted from only .35 percent (only one third of one percent) of the hardest hits, the study shows.

The study adds to growing research about concussions and other brain injuries, which have been getting increased attention at all levels of sports in recent years.

"Concussions are a hidden epidemic," said Kevin Guskiewicz, senior author on the study and chairman of the department of exercise and sport science in UNC's College of Arts & Sciences. "A concussion is not like a knee or an ankle that swells. It doesn't take a huge collision to cause a concussion."

A concussion is a brain injury that temporarily interferes with the way the brain works, according to the Mayo Clinic in Rochester, Minn. Concussions can affect memory, judgment, reflexes, speech, balance and coordination.

The most common concussion symptoms are confusion and amnesia, but concussions can be accompanied by headache, dizziness, ringing in the ears, nausea or vomiting or slurred speech. A blow to the head can cause the brain to slide forcefully against the inner wall of the skull. Bleeding in or around the brain and the tearing of nerve fibers can result.

But a concussion doesn't always happen when someone is hit into unconsciousness, Guskiewicz said.

"Some people believe you have to be knocked out to have a concussion, but one of our studies showed that only 8 percent of concussions result in people losing consciousness," he said.

The study was conducted with University of North Carolina football players, who wore special helmets fitted with a accelerometers from 2004 through the 2006 season. The accelerators measured the "G-force" of hits -- a measurement of acceleration against the earth's gravitational pull.

A roller coaster might produce 4.5g, a force pushing the rider back in the seat at four-and-half times the force of gravity.

An automobile crash test dummy can hit the windshield of a car, for example, at 100g in a 25 mph wreck.

A hit in football can jerk the head at 50g and a big hit might produce a G-force of 100g. One hit during the UNC study was measured at 168g.

What study looked at

The UNC study looked at three things:

* Identifying where hits were made.

* Measuring how hard concussion-causing hits are.

* Checking the recovery time following a concussion.

The results of the first part of the study were alarming because the most common site of a collision is the helmet, Guskiewicz said.

Leading with the helmet puts pressure on the head and neck, which can result in catastrophic injuries.

During the study, 11 players had a concussion and one player had two concussions.

Six of the 13 concussions came from hits to the crown rather than the sides, front or back of the helmet.

The study also found there is little difference in the rate of concussions by player position.

There was no appreciable difference in the concussion rate for offensive linemen and defensive backs, for example.

"We thought that defensive backs, where more speed is involved, would have a higher rate, but that's not what we found," Guskiewicz said.

And the study indicates that highlight-film big hits aren't necessary to sustain a concussion.

An earlier NFL study indicated that a blow that generated a 75 G-force would likely result in a concussion, but Guskiewicz said it became apparent early in the UNC study that researchers were getting different results.