Soccer is the most popular sport in the world, but soccer players are exposed to repetitive head impacts (RHI) when heading the ball. While heading is repeated thousands of times over a player's career, a possible brain cumulative effect might lead to neurodegenerative diseases. However, the lack of evidence explains the absence of prevention or protection for players. Our objective was to determine if playing soccer is associated with functional brain connectivity changes, depending on the exposure to RHI.

In this longitudinal study, a cohort of 16 semi-professional male soccer players, aged between 18 and 26 years old, were recruited from 2 clubs in Bordeaux city which participating in a French regional championship. Twenty age-matched male controls without a concussion history and which don’t practice any contact sport were also recruited for comparison. Functional Magnetic Resonance Imaging (fMRI) data were acquired for both groups before and after the 2016–2017 soccer season. A follow-up of the exposure to RHI in soccer group was realized thanks to the video of the games.

Soccer players demonstrated an increase of functional connectivity particularly between bilateral precentral region and fronto-temporal regions, in comparison with controls. Over the soccer play season, these increasing of functional connectivity was higher. The median of head impacts per player was 56 over the season, with no concussion. Exposure to RHI was associated with changes in functional connectivity between frontal and cerebellum regions.

Our data demonstrate changes of multiple brain networks at the resting state in trained soccer players, with greater changes over one play season. RHI effect or training effect could be implicated. Other imaging modalities are required to study possible microstructural and microvascular anomalies post RHI in soccer.