Heading in Soccer
Abstract & Commentary
Synopsis: Purposeful heading is unlikely to cause concussion and cognitive deficits in soccer players.
Source: Kirkendall DT, Garrett WE. Heading in soccer: Integral skill or grounds for cognitive dysfunction. Journal of Athletic Training. 2001;36(3):328-333.
In this article, Kirkendall and Garrett explain the mechanics of impact and heading a soccer ball, and discuss the mechanisms of head injury in soccer. They also review the literature related to neurological and neuropsychological findings in soccer players.
The mechanics of impact are based on the fundamental law of physics, ie, the relationship of F = ma, where F is force of impact, m is the mass of the object, and a is the acceleration of the object. Kirkendall and Garrett explain that a kicked soccer ball can travel more than 100 km/h, but the highest velocity that a player is likely to purposefully head a ball is from a punt, drop kick, or goal kick, at velocities ranging from 70-85 km/h. Soccer balls come in 3 sizes and weights, with the dimensions of the 3 balls designed for age groups of 6-9, 10-13, and older than 14. Prior to the 1970s, the ball was leather and absorbed water, which resulted in substantial increases in mass. The modern ball is synthetic and resistant to water absorption. Kirkendall and Garrett compare the gravitational forces that result from heading a soccer ball, impacts that result in American football, and impact forces during boxing. The "G" forces are far less in soccer, with the estimated impact of a soccer ball well below concussive levels.
Kirkendall and Garrett further explain that forces to the head in athletics are either linear, rotational, or a combination of both. Purposeful heading in soccer is primarily linear, and the head can withstand greater linear than rotational force. Unprepared ball to the head contact can lead to rotational forces, such as seen from "hooks" in boxing. Heading the soccer ball is a complex skill that requires precision timing, and it is designed to be active with trunk hyperextension and the chin tucked to the chest. Passive heading permits the ball to accelerate the head backward, which results in linear and transverse rotational forces.
Most head injuries in soccer result from the ball hitting an unprepared head, or from collisions with other players or the ground. The penalty area and midfield line create circumstances most likely to result in head injury. Higher rates of head injury in soccer are associated with higher and more competitive levels of play. Neurocognitive deficits have been reported from head injuries in soccer, and several Norwegian studies reviewed by Kirkendall and Garrett have suggested that heading is a cause of cognitive deficits.
Comment by David H. Perrin, PhD, ATC
The sport of soccer is immensely popular throughout the world, and its popularity has grown significantly in the United States. Parents and sports medicine specialists have become increasingly concerned about the potential of head injury and cognitive deficits resulting from heading. Some have proposed modifications to the rules related to heading, and others have proposed the use of helmets in soccer.
Kirkendall and Garrett propose in this paper that the actual heading exposure and details of the nature of the head-ball impact are unknown, and thus it is difficult to blame purposeful heading for the reported cognitive deficits in soccer. Indeed, they report that the vast majority of head injuries in soccer are known to result from head-to-head or head-to-ground impact, and any cognitive deficits are likely related to these mechanisms. They further point out that the findings of the often-cited Norwegian studies are questionable for several reasons. They studied players who participated in the 1960s and 1970s, before the advent of water-resistant balls. Other causes of cognitive deficits, such as alcohol abuse, were not considered, and the incidence of game-related head injuries was not described.
From what is currently known from the scientific literature, elimination of heading or the use of helmets would not appear to be indicated in soccer. In fact, American football serves as an example of how the wearing of helmets has led to increases in severity of injury in some respects. The best recommendations would seem to be that youth not attempt heading until attaining an appropriate level of maturity (most say 12 years or older), that the dimensions of the soccer ball be properly matched to the age of the participants, and that coaches tirelessly teach and emphasize correct technique. In the interim, carefully controlled prospective studies should assess the subconcussive impacts of purposeful heading on cognitive function and activities of daily living.
Dr. Perrin, Dean, School of Health and Human Performance, University of North Carolina - Greensboro, is Associate Editor of Sports Medicine Reports.