Just one season of football resulted in signs of damage to brain development for those youth players who have frequent impacts to the head, according to a study, CNN reported on Monday.

“Repetitive head impact exposure may have a cumulative effect in the rapidly developing brains of youth and high school football players,” said study co-author Gowtham Krishnan Murugesan.

The UT Southwestern Medical Center in Dallas study provided 60 football players between the ages of 9 and 18 who had no history of head trauma or developmental issues with a telemetry system that measures impacts to the head.

The players were put into two categories – those with high cumulative head impacts and those with low cumulative ones.

Before the season began, each child received a resting state functional scan, which was repeated at season’s end. The researchers were trying to see how exposure to repetitive hits affects the normal “pruning” process in the brain that occurs during adolescence.

After comparing those results to the player’s level of impact, the study found that youth in the high-impact group had damage after just one season to their pruning process – during which old, useless connections between nerves are supposed to be disposed of.

Disrupting this process means electrical and chemical connections within the brain do not work as well, which affects thinking skills, according to the Daily Mail.

The study adds to increasing evidence that regular blows to the head, even if they do not cause concussions, can result in long-lasting brain damage.