Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Kinesiology

Supervisor

Heath, Matthew

Abstract

A single bout of aerobic exercise improves executive function; however, the mechanism, or mechanisms, supporting this improvement remain unclear. One candidate mechanism is an exercise-mediated increase in cerebral blood flow (CBF) that enhances the efficiency of executive-related frontoparietal networks. To evaluate the link between exercise, CBF and executive function, three separate experiments were conducted. In the first study, separate 10-min sessions of moderate-to-heavy-intensity aerobic exercise, and a hypercapnic environment (i.e., 5% CO2) were implemented. The hypercapnic condition was included because it increases CBF independent of the metabolic demands of exercise. The second study investigated whether exercise intensity-specific changes in CBF differentially influence the magnitude of a postexercise executive function benefit. Accordingly, I measured CBF in conditions wherein participants completed separate 10-min sessions of light- (i.e., 25 Watts: W), moderate- (i.e., 80% estimated lactate threshold: LT), and heavy-intensity (i.e., 15% of the difference between LT and V̇O2peak) aerobic exercise. The third study measured CBF during separate passive and active light-intensity exercise conditions and evaluated putative immediate and sustained executive function benefits. My final study (i.e., Study 4) was developed to meet the challenges associated with COVID-related research restrictions and hence developed and evaluated an at-home tablet-based assessment of postexercise executive function. The first three studies demonstrated that an increase in CBF independent of the metabolic demands of exercise was associated with a postexercise improvement in executive function. The fourth study demonstrated that an at-home executive function assessment provides a reliable means to identify single bout postexercise benefits to executive function. The findings from my dissertation provide further evidence indicating that CBF is a candidate mechanism supporting postexercise executive function and demonstrate the utility of a novel executive function assessment that may be implemented in populations that are demo- and geographically under-represented in exercise neuroscience research.

Summary for Lay Audience

Single bouts of exercise improve brain health and cognition. How exercise improves cognition is unclear; however, an exercise-based increase in brain blood flow is thought to contribute to the improvement. To investigate this proposed link, I conducted three separate studies. First, I directly investigated the role of increased blood flow to the brain by having participants complete a 10-min exercise session and a same duration session wherein they breathed a higher-than-normal concentration of carbon dioxide. The inhalation of an increased concentration of carbon dioxide increases blood flow to the brain without requiring volitional exercise. Second, I examined whether exercise sessions of increasing difficulty – or intensity – change the amount of blood flow to the brain and thus provide an increased benefit to cognition. Participants’ brain blood flow was assessed as they completed three separate sessions of exercise at increasing intensities (i.e., light, moderate and heavy). Third, I compared for how long cognitive benefits persist following normal cycling, and a session wherein participants’ legs were moved ‘passively’ via a mechanized cycle ergometer. Finally, a fourth investigation completed during the COVID-19 provincial lockdown developed an iPad® app and deployed it to determine whether an at-home assessment provides a reliable basis to assess postexercise benefits in cognition. Results for the first three studies showed that changes to brain blood flow were related to improved cognitive function and this benefit was independent of exercise intensity and volitional muscle activity. The final study demonstrated that an iPad® app is a valid tool for measuring the link between cognition and exercise. Overall, the findings of my dissertation support brain blood flow as a mechanism for how exercise improves cognitive function and provides a novel tool to measure exercise-mediated changes in brain health in demo- and geographically underrepresented communities.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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