The Association of Physical Activity and Aerobic Fitness with Brain Structure and Functional Connectivity in Adolescents

Abstract

Over the past decades adolescents have experienced decreased aerobic fitness levels and insufficient physical activity levels. A sedentary lifestyle with little physical activity can be harmful to adolescents’ well-being and health. Despite this, the association between adolescents’ physical activity and aerobic fitness with brain health remains poorly understood. The primary purpose of this dissertation is to examine the association between physical activity and aerobic fitness with brain structure and function in 13–16-year-old adolescents. Additionally, earlier studies regarding the connections between physical activity and aerobic fitness with executive functions have been contradictory in youth. The second purpose of this dissertation is to investigate whether the brain’s white matter properties moderate the relationship between physical activity and aerobic fitness with core executive functions. The first study in this dissertation examined the association between moderate-to-vigorous physical activity and aerobic fitness (assessed using a 20-m shuttle run test) with the brain’s gray matter. The results show that higher level of aerobic fitness, but not physical activity, is related to smaller volume in the left superior frontal gyrus and larger volume in the left pallidum. The second study demonstrates that aerobic fitness, but not the physical activity, is associated with white matter properties in several tracts, but most robustly in the corpus callosum and the superior corona radiata. Furthermore, we found that the white matter moderates the connection of physical activity and aerobic fitness with working memory. The third study concentrated on the resting state functional connectivity of the brain. The findings show that adolescents’ physical activity, but not aerobic fitness, is related to local functional connectivity. However, they also reveal that neither of them is related to interhemispheric functional connectivity, as indicated by homotopic connectivity. Overall, the results of this dissertation show that both physical activity and aerobic fitness are related to an adolescents’ brains. Associations between brain properties and these two measures differ extensively. While aerobic fitness is especially associated with structural measures, physical activity is related to the functional measure at rest. Moreover, the findings related to the moderation analysis suggest that the varying previous results regarding the relationship of physical activity and aerobic fitness with the working memory might be explained by the varying levels of the brain’s white matter.