Downsides of downhill: The adverse effects of head vibration associated with downhill mountain biking on visuomotor and cognitive function

Vibration can be defined as an oscillatory movement around a stable point when the human body is supported by a vibrating surface or interacts with a vibrating feature. As the negative health effects of exposure to vibration have become a cause of concern, international and European standards have been developed to define thresholds and risk prevention in occupational exposure. An emerging issue is related to the transference of vibration from the feature-body interface to the level of the head that might be associated with changes in brain structure and function. Most studies investigating the effects of vibration on the human body are directed at physiological and musculoskeletal conditions, and relatively little attention has been given to vibration-induced cognitive problems. Difficulties of measuring subtle alterations in cognitive function might be one factor that could explain the limited number of studies.

In cycling, vibration is intrinsic to the activity due to the continuous interaction of the tyre surface and the terrain. Vibrational energy must be absorbed by mechanical structures of the bike and the cyclists' soft tissues to protect the axial skeleton and the central nervous system. It has been suggested that vibration during road cycling substantially exceeds occupational exposure limits (Edwards & Holsgrove, 2020), which indicates an elevated risk of adverse health outcomes. Initial evidence of the negative effect of head vibration experienced in downhill mountain biking (DH MTB) has been presented by Hurst et al, 2020 who found that four DH trials were sufficient to impair aspects of executive function such as psychomotor speed, reaction time, processing accuracy, and mental flexibility. Although the study compared the DH group's performance to an exercise-matched group without head accelerations and a control group, the study lacked direct quantification of head accelerations. Nevertheless, the authors previously demonstrated that rotational and translational head accelerations during DH MTB are higher than those reported in soccer, snow sports, contact sports and BMX (Hurst et al., 2018). Provided that repetitive head accelerations could compromise white matter integrity and neurocognition over the course of a season in football and ice hockey, DH riders might face an increased risk of sustaining irreversible brain injuries over an entire race season.

The primary aim of the project is to investigate how head vibrations associated with DH MTB influence cognitive function, oculomotor, and body movement control. A secondary aim is to elucidate the dose-response relationship between vibration exposure and brain function. For this purpose, a state-of-the-art VR paradigm will be developed, with high sensitivity, reliability, and validity for early identification of brain dysfunction. By gaining knowledge on the magnitude of head vibration and its potential influence on cognitive health, we can explore ways to reduce vibration and mitigate its harmful effect.