When France and Croatia go head to head in the World Cup final on Sunday, fans may want to see which team really has its head in the game.

Soccer players who head the ball more frequently may be more likely to experience slight balance problems, suggesting that repetitive head impacts could have the potential to cause subtle neurological deficits, according to a preliminary study by University of Delaware researchers. More research is needed to understand the long-term effects of these repetitive head impacts and potentially develop interventions to address them.

“Soccer headers are repetitive subconcussive head impacts that may be associated with problems with thinking and memory skills and structural changes in the white matter of the brain,” said study author John Jeka, a professor and chair of the Department of Kinesiology and Applied Physiology in the College of Health Sciences. “But the effect of headers on balance control has not been studied.”

The abstract will be presented July 21 at the American Academy of Neurology’s Sports Concussion Conference in Indianapolis.

The team of researchers led by Jeka studied 20 recreational and club soccer players from the UD community, Wilmington and Newark. Participants answered questions about the number of times they headed the ball and how often they played and practiced. The average player was 22 years old and reported heading the ball 451 times in the past year.

Players were asked to walk on a foam pad with their eyes closed. They were tested under two conditions -- one with electrodes placed behind their ears to make them feel like they were falling sideways and another without the stimulation. The electrodes make use of tool called galvanic vestibular stimulation that stimulates the nerves in the inner ear that affect balance.

The study found that players exposed to more repetitive head impacts were more affected by the vestibular stimulation while walking, suggesting subtle balance problems. For every 500 headers that a player reported, their foot placement and hip adduction responses slightly increased, Jaclyn B. Caccese, one of the study’s authors, said.

“At this point, it appears that frequent soccer heading may result in subtle balance impairments,” Caccese said. “The question is, do these really subtle effects matter and do they manifest to later life complications?”

Researchers want to understand the relationship between repetitive head impacts and balance, said Fernando V. Santos, another study author and a doctoral student in the Biomechanics and Movement Science interdisciplinary program. Because the balance problems are so subtle, the effects may not be clinically noticeable.

Santos and Caccese said more research is needed to learn about the effects of both repetitive head impact and concussion. A next step is to gain a better understanding of how people use sensory information to maintain balance following concussion and even mild head impact that does not result in acute symptoms of concussion. The hope is to understand why some people have balance problems after concussion and repetitive head impacts and how to treat it.

“Not everyone has effects from repetitive soccer heading,” said Caccese, a postdoctoral researcher in Jeka’s lab. “We need to identify individuals who do have it, identify why they have it and how to treat it - and if balance deficits persist, then we can design targeted interventions to rehabilitate those balance deficits.”

Study authors from the University of Delaware include Jeka, Santos, Caccese, Ian Sotnek, Elizabeth Kaye and Felipe Yamaguchi. This study was supported by the National Institutes of Health.