Soccer players suffer reduced memory and corticomotor functioning immediately after running heading drills, a new study finds. These changes are transient, and appear to subside within a day (video below).
The study of 19 amateur soccer players, aged 19 to 25, measured participants' neural and motor functions after heading 20 balls in 10 minutes.
The neural effects of heading were examined using a process called "motor evoked potentials." The process involves shooting a magnetic pulse through a participant's brain, and measuring the reaction times of the body. The video at the bottom of this article demonstrates the process.
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Figure 1: A snapshot of some of the data obtained by the study, which was published in EBioMedicine. It shows that the amount of time between the magnetic pulse (dashed line) and the brain returning to normal (arrow) increased immediately after heading drills (b) compared to immediately before (a). This is called the "cortical silent period." The data shows that the brain takes longer to return to normal after heading drills.
In addition to this measurement of what is called the "cortical silent period," participants were tested on reaction time, long and short term memory, attention, and rapid visual processing. According to the study, "heading only significantly affected memory function; the remaining [tests] did not show significant heading-associated decrements compared to baseline assessments."
These results indicate that after sustaining sub-concussion impacts to the head, the brain releases a chemical signal called GABA, which "can interrupt or block certain brain activity and potentially make muscles more difficult to control," according to an article in The Conversation written by the study's authors. GABA is "the most powerful inhibitor in the brain's motor system."
"If there is more inhibition in the brain immediately after heading the ball," the authors write, "this could affect control of the muscles which may impair performance and expose the player to greater injury risk."
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This is the first study to explore the immediate effects of heading. The scientists say that more research is needed to determine whether the immediate effects accumulate over the lifetime of a soccer player.
According to a review of soccer related medical studies conducted by NCBI, 81 percent of former players have "mild to severe deficits in the areas of attention, concentration, memory and judgment."
A 1998 study on concussions in soccer players found that most concussions were a result of a player colliding with a member of the opposing team, and none resulted from intentional heading, according to NCBI.