Differences in height, weight and technique may make high school football tackles more risky to the head and spine than those that occur in college football, a new study shows.

The report, “Head Impacts During High School Football: A Biomechanical Assessment,” published in the July 2009 issue of The Journal of Athletic Training, analyzed the biomechanics of football tackles to better understand the high risk of concussions and serious cervical spine injuries faced by high school players.

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The study, from researchers at the University of Illinois at Urbana-Champaign, studied 35 high school varsity players who wore helmets equipped with sensors to measure the impact and force of tackles on the head and neck. During the 2007 football season, the researchers collected data from 68 sessions, including 55 practices and 13 games. They analyzed a total of 19,224 impacts and measured the intensity and duration of the impact, the linear and rotational acceleration (the speed at which the body or head moves after a hit), and the “jerk” or change in acceleration. The data were compared with those from similar studies of college football players.

Not surprisingly, the data showed that defensive linemen had the highest number of impacts, although only slightly more than offensive linemen. They also found that tackles during games were far more forceful and severe than those during practice.

But most importantly, the study showed that the average linear accelerations from a high school football tackle exceeded those at the college level. Impacts to the top of the head had the greatest speed and force. Among high school players, blows to the front of the helmet were about 10 percent more common and carried 3 more “Gs” of force than among college players.

The study authors said differences in physical maturity, neck strength and endurance among high school athletes may be a factor in the increased injury. They noted that the comparison group of college athletes weighed about 30 pounds more, on average, than the high school students, but were only about 1.2 inches taller. That may result in a “more developed musculature system that is better able to control head motion after impact,” the researchers noted.

The researchers said the technique may also be an issue, and the finding highlights the need for coaches to teach proper tackling techniques, so that the athlete keeps his head up and avoids contact with the top of the helmet.

While the researchers said it is not clear whether the small differences in linear acceleration between high school and college athletes make a difference in risk for concussion or other injury, there are other reasons high school football may be less safe. More than half of high schools don’t have medical staff on the football field, they noted.

About 5 to 6 percent of football players and about 8 percent of National Football League players suffer concussions or other forms of brain injury. (That translates to 3,264 to 4,284 of the nearly 68,000 collegiate players and 130 of the 1,700 N.F.L. athletes.) Among the 1.2 million teens who play high school football, the group that accounts for most sports-related concussions, between 4 and 6 percent sustain concussions, or about 43,200 to 67,200 injuries a year. However, the real incidence is probably higher, as more than half of high school athletes who suffer concussions are suspected of failing to report the injury, researchers say.