They're younger, and probably smaller, but high school football players sustain more forceful head impacts than college athletes, putting them at higher risks for severe injuries, according to a new study.

The reason? It may be because of how the younger players are using their heads, you might say.

In a study involving 32 high school varsity players, Dr. Steven P. Broglio from the University of Illinois at Urbana-Champaign and his colleagues placed accelerometers in athletes' helmets to calculate the force with which they were being hit in the head, the direction and duration of the impact, and related factors.

"We kind of expected that side-to-side head impacts" - perhaps coming unexpectedly from other players - "would have the highest force," Broglio told Reuters Health.

Instead, he continued, "We were surprised to see that the largest magnitude (of force) was from impacts to the top of the head."

Broglio isn't sure, but suspects that top-of-the-head impacts are so forceful because the younger players may be leading with their heads, using them almost like battering rams.

"Novice players have a tendency to hit with the top of their heads," he said. "They need to keep their heads up," and "coaches need to emphasize proper tackling techniques."

As they report in the Journal of Athletic Training, the investigators also found, during games and practices over the course of a season, that head impacts in the high school football players were greater than what college players experience.

Differences in physical maturation, strength, and endurance might explain why the high school players are getting hit harder than their college counterparts.

Whatever the reason, the difference probably increases the high school athletes' risk for injury, particularly for concussions and severe injuries of the upper spine.

On the high school team, offensive and defensive linemen "sustained the lowest-magnitude impacts but the highest number of impacts during games and practices," according to the investigators.

The researchers don't know how their findings relate to concussion occurrence. In a year or so, however, Broglio expects to have more data on the amount of force necessary to cause injuries.