Abstract
Repetitive hits to the head that do not result in concussions are of increased concern to sport science and the sporting community. The term 'subconcussion' is widely used, not well understood, and requires further clarity. Therefore, the purpose of the study was to systematically review the literature and address two objectives: 1) To determine how 'subconcussion' is characterized in the current literature and 2) to evaluate the evidence on subconcussive impacts in sport. CINAHL, EMBASE, MedLine, PsycINFO, SportDiscus, and Web of Science were searched for articles that sought to assess subconcussive impacts or outcomes related to non-concussive head impact exposure in sport. A total of 1966 articles were screened, with 56 meeting the inclusion criteria and assessed for quality. The studies varied in focus from neurobiology, neuropsychology, to impact exposures. The main finding of the review was that repetitive head impacts in male athletes was associated with functional and microstructural deterioration. Whether these changes represent injury is unclear. Conclusions about female athletes could not be drawn because they were underrepresented in all categories of study. The term 'subconcussion' itself was inconsistently used across the literature, and was poorly defined. 'Subconcussive impacts', 'head impacts', or 'repetitive hits to the head', without inference to injury, may be more appropriate and less confusing. Future research is needed to investigate the phenomenon more thoroughly, and to advance our understanding of how exposure to head impacts affects the brains of athletes in the short and long-term.Acknowledgments: We would like to acknowledge Julian Clarke