Head impacts, not age, determine brain's white matter changes in football players

Reviewed by Kate Anderton, B.Sc. (Editor)Nov 5 2019

Magnetic resonance imaging (MRI) scans performed at the beginning and end of football season show significant changes in the brain's white matter in both youth and high school football players, reports a study in Clinical Journal of Sport Medicine. The journal is published in the Lippincott portfolio by Wolters Kluwer.

White matter alterations over the season are greater in high school football players, reflecting their higher volume and magnitude of head impact exposure, according to the new research by Gregory D. Myer, PhD, of Cincinnati Children's Hospital Medical Center and colleagues. They write,

Our results did not confirm recent speculation that younger children are more susceptible to the deleterious effects of repetitive head impacts compared with their older counterparts."

Head impacts, not age, are main determinant of brain white matter changes

The study included 12 youth football players (average age 13 years) and 21 high school football players (average age 17.5 years). Both groups underwent two brain MRI scans: one preseason (before the first football practice) and one postseason (after the last regular season game).

Using a specialized MRI technique called diffusion tensor imaging, the before-and-after scans evaluated head impact-related structural alterations in the white matter. In both groups, head impacts with forces greater than 10 G were recorded using a helmet-mounted accelerometer. The extent of white matter alterations was compared between the two age groups.

High school football players sustained more head impacts, and more impacts with higher G-forces, compared to youth football players. One youth football player and three high school players sustained sport-related concussions during the season. In both groups, the concussion rate was roughly two per every 1,000 athlete exposures.

From the preseason to postseason MRI scans, the high school football players had reductions in three out of four MRI measures of white matter alterations. Consistent with previous studies, the changes were detected across areas of the brain.

By comparison, the youth football players had significant changes in just one of the four MRI measures, called axial diffusivity (AD). The changes in AD were more limited in extent in the youth compared to high school players; in both groups, the changes were region-specific. After adjustment for head impacts, the average reduction in AD was about 2.5 percent in high school football players versus 0.4 percent in youth players.

That's in contrast to recent reports suggesting that younger athletes might be more vulnerable to the harmful effects of head impacts, potentially at critical times in brain maturation during childhood. "Youth football participation has decreased in recent years, due, in part, to highly publicized concerns regarding sports-related concussions," Dr. Myer and coauthors write.

Their study provides the first prospective longitudinal and objective data comparing head impact-related brain MRI changes in youth versus high school football players. The results show that both age groups white matter alterations during a single football season, with the changes appearing to be most related to the volume and severity of head impacts and not the age of the athlete's exposure.

"Given these described trends, it is sensible to expand research towards strategies that can mitigate the magnitude of force absorption in the brain from head impact exposure for athletes of all ages," Dr. Myer and colleagues conclude. They emphasize the need for further studies– including data on more athletes in various high-risk sports over multiple seasons of play – to further clarify the limited "age-dependent vulnerability of white matter to head impact exposure in football."