In a new study, researchers at the University of Michigan set out to answer that question. They monitored 33 NCAA Division I football players using a device custom-fitted into the players' shoulder pads that had both a GPS receiver and an accelerometer. They measured the intensity and number of impacts, along with their distribution over the players' bodies. Then they sorted this data based on the players' positions.
The impacts were measured in G-force. One G is equal to the force of Earth gravity, so 5 G's is five times the force of gravity. According to NASA, 3 G's is the amount of force it takes to pin people to the walls of spinning rides often seen at carnivals. A race car braking and turning is under about 5 G's of force, said Dennis K. Lieu, a professor of mechanical engineering at the University of California, Berkeley, in an email interview with Live Science. Lieu has spent about 20 years studying blunt trauma injury in sports; he was not involved in the new study. [
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The researchers found the running backs in the study — the men generally tasked with carrying the ball — experienced more "severe" impacts (above 10 G's) than all other offensive positions, although not a statistically significant number more than quarterbacks, according to the findings published May 21 in the Journal of Strength and Conditioning Research. But at the same time, the running backs recorded fewer "heavy" impacts (7.1 to 8 G's) than either wide receivers or offensive linemen.
The researchers said that the severe impacts that running backs sustain could be the result of being tackled by multiple players while running at a high speed, or receiving a direct, head-on tackle from an opponent who is running at a high speed.
The wide receivers in the study experienced the most "very light" and "light to moderate impacts," among the offensive positions. These impacts ranged from a force of 5 to 6.5 G's. Offensive linemen also experienced significantly more very light impacts than either running backs or quarterbacks.
Among the defensive positions, defensive tackles experienced more moderate to very heavy (6.6 to 10 G's) hits than any other defensive position. The players in this position also recorded more light to moderate (6.1 to 6.5 G's) impacts than all other defensive positions. [
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This wide range of the forces of the hits that defensive tackles take is likely due to their high amount of physical contact with several opposing players during each play, the researchers wrote in their findings.
Defensive ends engaged in more severe impacts than any other defensive position, but the difference was not significant, according to the study.
Defensive backs and linebackers were subject to the most very light impacts (5 to 6 G's).
The study categorized the hits from very light to severe, but these labels don't signal potential for injury, Lieu said.
"At this time, there are no conclusions that have been drawn about any long-term health risks that may result from repeated exposures to such accelerations," he said. He noted, however, that the authors cited a 2012 study, co-authored by one of the same authors who did the new research, which found that impacts exceeding 7 G's were associated with decreases in neuromuscular performance after rugby competitions.
