Fitness, but not physical activity, is related to functional integrity of brain networks associated with aging

Abstract

Greater physical activity and cardiorespiratory fitness are associated with reduced age-related cognitive decline and lower risk for dementia. However, significant gaps remain in the understanding of how physical activity and fitness protect the brain from adverse effects of brain aging. The primary goal of the current study was to empirically evaluate the independent relationships between physical activity and fitness with functional brain health among healthy older adults, as measured by the functional connectivity of cognitively and clinically relevant resting state networks. To build context for fitness and physical activity associations in older adults, we first demonstrate that young adults have greater within-network functional connectivity across a broad range of cortical association networks. Based on these results and previous research, we predicted that individual differences in fitness and physical activity would be most strongly associated with functional integrity of the networks most sensitive to aging. Consistent with this prediction, and extending on previous research, we showed that cardiorespiratory fitness has a positive relationship with functional connectivity of several cortical networks associated with age-related decline, and effects were strongest in the Default Mode Network (DMN). Furthermore, our results suggest that the positive association of fitness with brain function can occur independent of habitual physical activity. Overall, our findings provide further support that cardiorespiratory fitness is an important factor in moderating the adverse effects of aging on cognitively and clinically relevant functional brain networks.

Associations among executive function, cardiorespiratory fitness, and brain network properties in older adults

“…This result can also be instinctively understood. Higher fit older adults achieve better cognitive functioning, which should be regulated by the structural and functional states of the brain202427, and this can be captured even in a resting state35. We demonstrated such an association in older adults in topological rsFC data, especially for global efficiency.…”

“…Using rsfMRI, researchers have demonstrated that substantial changes of rsFC occur in normal and pathological aging3334. A positive association between cardiorespiratory fitness and rsFC was recently demonstrated in several cortical networks of older adults35.…”

Aerobic Exercise Intervention, Cognitive Performance, and Brain Structure: Results from the Physical Influences on Brain in Aging (PHIBRA) Study

“…As the aerobic exercise group improved their aerobic fitness considerably compared to the control group one could have expected to find an effect from aerobic fitness in dlPFC over time, explaining also the improved cognitive performance, considering that “Cognitive score” predicted dlPFC thickness both at baseline and change over time in the aerobic group. However, one explanation is that the exercise-induced improvements in cognitive performance immediately after a period of training is not mainly due to gray matter changes, but may depend on altered cardiovascular responses (Colcombe et al, 2004; Voelcker-Rehage et al, 2011), white matter changes (Voss et al, 2013; Oberlin et al, 2016), functional connectivity (Voss et al, 2010, 2016), brain-derived neurotrophic factor (Leckie et al, 2014), or other molecular processes. Wheel-running for example, has been associated with alterations in dopaminergic markers in striatum (MacRae et al, 1987; Meeusen et al, 1997; Kim et al, 2016), and considering the influence of dopamine both on prefrontal and striatal function in relation to executive control functions, (Frank and O'Reilly, 2006; Cools and D'Esposito, 2011; D'Esposito and Postle, 2015) this could be a potential pathway for exercise-induced improvements in cognition.…”

An Objective Method to Accurately Measure Cardiorespiratory Fitness in Older Adults Who Cannot Satisfy Widely Used Oxygen Consumption Criteria

“…no specified criteria)[12, 32, 33], using one physiological variable (i.e. HR, RER)[13, 34, 35], or reporting some combination of variables [14, 36, 37]. For this project, we chose the ACSM guidelines because they provide an empirically established standard for CRF testing [28].…”

“…A common solution is to relax V̇O 2max criteria (plateau in oxygen consumption) and use the level of oxygen consumption at peak exercise (V̇O 2peak ) as the measure of CRF [11]. However, the criteria for judging the validity of a V̇O 2peak test varies throughout the aging literature [12–14] and the consequences of using more liberal criteria for estimating CRF in older adults have received inadequate attention [7, 15]. …”