Soccer players beware: you might want to think twice before heading the ball.
A study published in the June 11, 2013 issue of the journal Radiology, finds that players who head the ball frequently score worse on memory tests and are at higher risk of brain abnormalities than those who head the ball less often.
In soccer, “heading” is an offensive or defensive move in which a player uses his or her unprotected head to deliberately strike the ball and direct it during a game. On average, most players head the ball 6 to 12 times during competitive games, where balls can travel up to 50 miles per hour (80 kilometers per hour). Heading is even more frequent during practice sessions: it’s not uncommon during heading drills for players to perform 30 or more headers in a short span of time.
The effects of sports-related concussions on cognitive functions have been well documented, and substantial media attention has been devoted to the cognitive impairment seen in retired football players in particular. But the clinical significance of less severe “subconcussive” impacts such as those associated with heading in soccer has not been investigated as thoroughly, and there is no consensus on how dangerous such impacts may be.
A Heading Threshold
To investigate the effects of subconcussive trauma on brain function, neuroradiologist Michael Lipton and his colleagues performed diffusion tensor imaging (DTI), an advanced MRI-based imaging technique that measures the uniformity of water movement (called fractional anisotropy) throughout the brain on 28 men and nine women soccer players (median age 31) recruited from amateur leagues in New York City. They also gave the players memory tests.
Lipton, who is at the Albert Einstein College of Medicine in New York City, and his team hypothesized that they would detect a “threshold” for heading, above which the risks of brain abnormalities and memory impairments would increase. They believed that if their hypothesis were confirmed, it would have major consequences for public health, the authors write in their paper.
The soccer players in the study were asked to recall about how many times they had headed the ball over the past 12 months. Most of them reported having done so hundreds of times, and the count for some players was in the thousands. The median heading count for the group was 432, while the range was from 52 to 5,400.
When the researchers looked at the DTI scans of the players, they found that some of them showed brain abnormalities. The abnormalities occurred mainly in the white matter of three regions of the brain that are associated with attention, memory, sensory inputs, visual and spatial processing, and other cognitive functions.
The team also found evidence of thresholds for damage in the three brain regions investigated, thus confirming their hypothesis. One brain region, for example, had a header threshold of 850 — that is, players who headed the ball at least 850 times were more likely to show abnormalities in this part of the brain than those who fell short of the threshold. For the other two brain regions, the thresholds were about 1,300 and 1,550 headers.
The affected brain regions lie near the back of the head—opposite the typical point of impact of a header. This might seem counterintuitive at first, but the researchers hypothesize that brain “recoil” could explain the finding “When there is a head impact, the brain sloshes back and forth inside the head,” Lipton told ScienceNews. When a player performs a header with the front of the head, Lipton added, the brain presses against the front of the skull momentarily but then slams into the back of the skull.
The researchers also conducted memory tests on the players. They found that the nine players with the highest header count scored worse on average than the nine who had the fewest. The researchers estimated that the threshold for memory loss was about 1,800 headers.
The new findings add to a growing body of evidence that not only sports-related concussions but also less severe “sub-concussions” can lead to long-term memory impairment, reduced attention span and impaired concentration. “These changes are subtle,” Inga Koerte, a radiologist at Harvard Medical School and Brigham and Women’s Hospital, both in Boston, Massachusetts, told ScienceNews. “But you don’t need a concussive trauma to get changes in the microstructure of your brain,” said Koerte, who was not involved in the study.
In a previous study, Koerte had found that even soccer players who had never been diagnosed with a concussion had more white matter abnormalities than swimmers did. “While we do not yet know what these changes mean, soccer players should be aware that they may be putting themselves at some risk for developing brain injuries,” Koerte said in a recent interview with the German Center for Research and Innovation.
The discovery of header thresholds for brain abnormalities and memory impairment could be used to create safety guidelines for soccer players, Lipton and his coauthors write in their paper. For example, “prospective monitoring of exposure at the team level, perhaps to be termed head counts, could identify a point at which a player’s heading should be curtailed for a specific recovery period,” they write. The researchers noted that such an approach is already being used in youth baseball, where pitchers are limited to a certain number of pitches to reduce the risks of arm and shoulder injuries.
Lipton and his colleagues also envision genetic tests that players could take to help reduce their risk of brain injuries. For example, a player found to have a genetic variant that had been linked to a greater risk for heading-related traumatic brain injuries might be advised not to head. The authors observed that further research would help in developing “evidence-based protective strategies that can ensure the future of safe soccer play.”
The soccer study asked players to report on how much heading they had done. Many studies involve such “self-reporting,” but questions can be raised about self-reported data. What problems might be associated with self-reporting? How might one try to obtain heading data without relying on self-reporting?
The study correlates possible negative consequences of heading with the number of times the ball had been headed within a certain period of time (in this case a year.) How might one test whether the overall number of headers is the most important factor, as opposed to, say, differences in players’ skulls or other physical features. Heading the ball has also been linked to neck injuries which you can read about on thesciencepost.