Investigating the role of physical activity in promoting neurological health following mild traumatic brain injury

Shaun Markovic

Mild traumatic brain injury (mTBI) can lead to a range of acute and chronic health-related challenges. Physical activity, especially the prescription of post-mTBI exercise, has emerged as a mechanism to promote recovery and improve neurocognitive outcomes. Specifically, recent research has shown that the administration of individually tailored aerobic exercise protocols (i.e. by target heart rate) is effective in accelerating symptom resolution following acute mTBI. However, many individuals exposed to mTBI in the wider community may not have access to rehabilitation settings where tailored exercise programs can be administered by a clinician. As such, there is a need to better understand the factors that influence peoples’ decision to engage in exercise while recovering from mTBI, as well as the impact that self-regulated exercise patterns have on recovery outcomes in the general population. Exposure to repetitive mTBI is also increasingly linked to neurodegeneration later in life, while maintaining a high level of cardiorespiratory fitness could provide a degree of neuroprotection. Consequently, it is also imperative to continue to investigate how mTBI exposure and variations in cardiorespiratory fitness interact to affect later-life brain health, particularly in non-athlete older adults. In Chapter 2, a comprehensive narrative review examined the therapeutic value of lifestyle-based modifications such as exercise as a mechanism to promote neurological recovery following mTBI, specifically for older adults. Chapter 3 subsequently explored factors that could influence post-mTBI exercise engagement, along with its subsequent impact of exercise on time to symptom resolution, in a community-based sample of 201 Australians reporting a mTBI within the last 18 months. Sustaining a sports-related mTBI significantly increased the odds of engaging in exercise while recovering. Contrary to the prevailing literature, respondents who exercised also had lower odds of their symptoms resolving completely at one-month post-injury, although subset analysis also indicated that participants who resumed exercise within the first week had higher odds of recovery at one-month. The results suggest that individually tailored protocols of exercise may be necessary to reduce the risk of chronic symptom development. Chapter 4 investigated the complex interaction between mTBI exposure, brain volume measured later in life (aged 65+) and cardiorespiratory fitness. Seventy-nine older adult, 25 of which had experienced at least one lifetime mTBI, completed VO2peak testing and magnetic resonance imaging. Older adults with mTBI history were found to have a significantly larger grey matter volume than no-mTBI control participants. A subsequent moderation analysis found that cardiorespiratory fitness level did not influence the mTBI-grey matter volume relationship, but there was preliminary evidence to suggest it may modify white matter volume depending on the level of previous mTBI exposure. The efficacy of retaining or increasing cardiorespiratory fitness levels later in life to provide protection against neurodegeneration precipitated by neurotrauma requires further investigation. The data gathered from the studies conducted in Chapter 3-4 contributed to the development of a randomised controlled trial protocol for the administration of an acute exercise intervention for older adults following recent mTBI exposure, which is detailed in Chapter 5. The protocol was also based on preliminary data gathered from a study into physical activity patterns and recovery from acute mTBI in older adults that was halted by the COVID-19 pandemic. In sum, this PhD thesis provides key insight into the relationship between exercise, neurocognitive health and the downstream effects of both acute and chronic mTBI, both from a theoretical and practical perspective. The potential for endogenous, self-regulated exercise to negatively influence time to symptom resolution after acute injury is an important consideration for rehabilitative health professionals. Moreover, the reported association between mTBI history and variations in later-life brain volume underscores its potential to trigger changes in the ageing brain, while increased cardiorespiratory fitness could also concurrently modify white-matter related pathology. There is clear scope for continued investigation into the utility of exercise-based interventions for older adults, both to promote recovery from acute mTBI and to protect against chronic injury-linked declines in brain health.

Investigating the role of physical activity in promoting neurological health following mild traumatic brain injury

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