ABSTRACT Objectives Cognitive reserve is hypothesised as a protective process against cognitive impairment arising from brain injury. Different life experiences provide a shield against the effects of brain changes to modulate or delay the expression of cognitive impairment. The current study investigated the long-term neuropsychological outcome of retired, predominantly equestrian, athletes. Methods Neuropsychological performance of participants with a history of concussion was compared to age-matched controls using Principle Components Analysis (PCA) regression, adjusted for participant characteristics. Premorbid function was used as an index of cognitive reserve. Results Three components were identified that explained greater than 95 percent of the variance in 14 neuropsychology tests; the first component (PC1) explained 87 percent of the variance. A regression model on PC1 identified an association between concussion and PC1, with lower scores in concussed participants with lower premorbid function. Conclusions A history of concussion is associated with lower neuropsychological performance, and this is more pronounced in individuals with lower premorbid functioning, an indicator of cognitive reserve.

The authors have declared no competing interest.

The ICHIRF project is currently philanthropically funded by Godolphin Racing, the Injured Jockeys Fund (UK), the Irish Injured Jockeys Fund, the Players Foundation, the National Football League (US), the Concussion Foundation, the Racing Foundation, the British Association of Sport and Exercise Medicine as well as private donations.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Ethical approval was obtained from St Marys University Twickenham Waldgrave Road London TW1 4SX UK on 1st June 2015 SMEC_2015-16_53 SMEC_2016-17_115 and SMEC_2017-18_051. Ethical approval was obtained from St Marys University, United Kingdom. All participants provided written informed consent. The trial was registered as ISRCTN 11312093. SMEC= St Marys' Ethical Committee

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All data will be available at the end of the 10 years study 2015-2025 upon reasonable request to the authors