The acute effects of non-concussive head impacts in sport: A randomised control trial.

Abstract

Background Head impacts, particularly, non-concussive impacts, are common in sport. Yet, their effects on the brain are poorly understood. Here, we investigated the acute effects of non-concussive impacts on brain microstructure, chemistry, and function using magnetic resonance imaging (MRI) and other techniques. Results Fifteen healthy male soccer players completed this randomised, controlled, crossover trial. Participants completed a soccer heading task (‘Heading’; the Intervention) and an equivalent ‘Kicking’ task (the Control); followed by a series of MRI sequences between ~ 60–120 minutes post-tasks. Blood was also sampled, and cognitive function assessed, pre-, post-, 2.5 hours post-, and 24 hours post-tasks. Brain chemistry: Heading increased total N-acetylaspartate (p = 0.012) and total creatine (p = 0.010) levels in the primary motor cortex (but not the dorsolateral prefrontal cortex) as assessed via proton magnetic resonance spectroscopy. Glutamate-glutamine, myoinositol, and total choline levels were not altered in either region. Brain structure: Heading had no effect on diffusion weighted imaging metrics. However, two blood biomarkers expressed in brain microstructures, glial fibrillary acidic protein and neurofilament light, were elevated 24 hours (p = 0.014) and ~ 7-days (p = 0.046) post-Heading (vs. Kicking), respectively. Brain function: Heading decreased tissue conductivity in five brain regions (p’s < 0.001) as assessed via electrical properties tomography. However, no differences were identified in: (1) connectivity within major brain networks as assessed via resting-state functional MRI; (2) cerebral blood flow as assessed via pseudo continuous arterial spin labelling; (3) electroencephalography frequencies; or (4) cognitive (memory) function. Conclusions This study identified chemical, microstructural and functional brain alterations in response to an acute non-concussive soccer heading task. These alterations appear to be subtle, with some only detected in specific regions, and no corresponding functional deficits (e.g., cognitive, adverse symptoms) observed. Nevertheless, our findings emphasise the importance of exercising caution when performing repeated non-concussive head impacts in sport. Trial registration ACTRN12621001355864. Date of registration 7/10/2021. URL https//www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=382590&isReview=true