Position-dependent white matter microstructural differences in amateur soccer players: a multi-shell diffusion MRI...

To exploratorily evaluate whether long-term exposure to repetitive subconcussive head impacts is associated with position-related patterns of white matter microstructural variation in amateur soccer players using multi-shell diffusion MRI.

This prospective observational study included 43 male amateur soccer players (defenders, n = 17; midfielders, n = 14; goalkeepers, n = 12), aged 18-27 years, each with ≥ 10 years of playing experience. Player position was defined as the primary registered position reported by the participant's club and confirmed by self-report as the predominant playing role over the preceding decade. Participants reporting frequent position switching or hybrid tactical roles were excluded to reduce positional overlap. Diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI) metrics were analyzed using tract-based spatial statistics. Given the modest sample size and the use of player position as an indirect proxy for repetitive head-impact exposure, the analytical framework was defined a priori as exploratory and hypothesis-generating.

Defenders demonstrated more widespread white matter microstructural differences compared with midfielders, characterized by reduced fractional anisotropy and neurite density index and increased radial and mean diffusivity across multiple association, projection, and commissural tracts (P < 0.05, TFCE-corrected). Comparisons involving goalkeepers revealed fewer and more spatially restricted alterations. No cerebral microhemorrhages were detected on susceptibility-weighted imaging. Neurocognitive performance did not differ significantly among groups.

Within the constraints of an exploratory design and operational position definitions, multi-shell diffusion MRI identified position-associated patterns of white matter microstructural variation in amateur soccer players, with defenders showing more extensive alterations. These findings should be interpreted cautiously and primarily serve to inform future studies employing larger samples, objective exposure metrics, and longitudinal designs.