Is the brain of fitter individuals different from that of less fit individuals? Yes, several investigations support that there are indeed important structural differences in the brain in people with different physical fitness levels.
As an example, a recent study conducted by our group in 100 overweight-obese children explored the whole brain and observed that the children with higher aerobic fitness (capacity of a person to do exercise for a long time and efficiently, also known as cardiorespiratory fitness) have higher volume in 9 cortical and subcortical brain regions relevant for cognition, executive function, and academic achievement . In addition, we observed in a different study and group of children that aerobic fitness level was associated with the shapes of subcortical brain regions, showing therefore a link between physical fitness and brain morphology . Similarly, other researchers have observed that hippocampus and dorsal striatum, key brain structures responsible for memory and other high cognitive functions, are markedly larger in fitter kids compared with less fit kids [3,4].
Image taken from: https://pixabay.com/es/salud-mental-la-formaci%C3%B3n-del-cerebro-2313426/
But differences in brain volumes according to physical fitness are not only observed in the growing brains of children, but also in adults and in older adults in which brain volume is known to shrink as a person ages. Several investigations have consistently shown that hippocampus volume is larger in fitter older adults than in their less fit peers . However, even more important are the results of another study which demonstrated that 1 year of aerobic training in older adults did not only attenuate the natural decline in hippocampus volume observed in the control group that did not train, but did even successfully reverse the natural trend, increasing hippocampal volume by 2% and leading to improvements in memory function .
Collectively, existent evidence concisely supports that individuals with a better aerobic fitness level, have more developed certain regions of the brain, which in turn has shown to positively influence cognition. Therefore, there is emerging evidence suggesting that to exercise and be in a good fitness level is healthy not only for the body, but also for the brain and cognition. Thus, as stated in the title of a landmark review article in this topic … “Be smart, exercise your heart”.
Francisco B. Ortega, Adrià Muntaner-Mas, Antonio Martínez-Nicolás and Irene Esteban-Cornejo
The PROFITH research group: http://profith.ugr.es/
University of Granada, Spain.
 Esteban-Cornejo I, Cadenas-Sanchez C, Contreras-Rodriguez O, et al. A whole brain volumetric approach in overweight/obese children: Examining the association with different physical fitness components and academic performance. The ActiveBrains project. Neuroimage 2017;159:346-354.
 Ortega FB, Campos D, Cadenas-Sanchez C, et al. Physical fitness and shapes of subcortical brain structures in children. Br J Nutr 2017:1-10.
 Chaddock L, Erickson KI, Prakash RS, et al. A neuroimaging investigation of the association between aerobic fitness, hippocampal volume, and memory performance in preadolescent children. Brain Res 2010;1358:172-183.
 Chaddock L, Erickson KI, Prakash RS, et al. Basal ganglia volume is associated with aerobic fitness in preadolescent children. Dev Neurosci 2010;32:249-256.
 Erickson KI, Prakash RS, Voss MW, et al. Aerobic fitness is associated with hippocampal volume in elderly humans. Hippocampus 2009;19:1030-1039.
 Erickson KI, Voss MW, Prakash RS, et al. Exercise training increases size of hippocampus and improves memory. Proc Natl Acad Sci U S A 2011;108:3017-3022.
 Hillman CH, Erickson KI, Kramer AF. Be smart, exercise your heart: exercise effects on brain and cognition. Nat Rev Neurosci 2008;9:58-65.