Being active and fit slows the impact of aging on the brain. A diverse set of mechanisms are involved, and, as is often the case in these matters, it is far from clear as to which of these mechanisms are the most important. Fitness helps to maintain the vascular system in a better shape, keep levels of chronic inflammation lower, causes mild stress that makes cells throughout the body undertake greater maintenance activities, ensures that the gut microbiome ages more slowly, better maintaining the production of metabolites that affect neurogenesis. And so forth - the list goes on.
Nowadays, we are constantly bombarded by media, physicians, and other health professionals to engage in physical/sports activities to reduce physical/psychological stress, improve our health, and reduce the risk of chronic disease. The literature has clearly demonstrated aerobic fitness as one of the best indicators of resilience. This is supported by evidence from a number of studies showing that physical fitness confers physiological and psychological benefits and protects against the development of stress-related disorders, as well as improves cognition and motor function that are a consequence of aging and of neurological disorders.
Although we have learned about neurobiological mechanisms of physical fitness from the neuroplasticity and neuroprotection that confer resilience, these effects and mechanisms are diverse and complex and need to be further explored. However, we can summarize that exercise modulates several mechanisms that may increase brain health and counteract brain disorders. Exercise positively influences neuronal reserve by increasing BDNF expression which promotes neurogenesis and synaptic plasticity, reduces oxidative stress and inflammation, and enhances cerebral and peripheral blood flow, which stimulates angiogenic factors that lead to positive changes in the structure and morphology of brain vasculature. All these changes shape brain activity and serve as a buffer against stress-related disorders.
While several models of physical activity or exercise may impact positively on brain resilience such yoga, dance, martial arts, etc., in this review we aimed to focus mainly on the effects of aerobic exercise of low and moderate intensity or resistance exercise. Thus, physiological markers including heart rate variability, blood pressure, and cortisol might be regularly used as indicator of stress to determine the impact of exercise on brain resilience. Some examples of stress systems are the immune-inflammatory system, the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system. Disturbance of these systems could lead to hyperactivity of the HPA-axis, sympathetic activation, and systemic inflammation.
However, there are still unanswered questions concerning (1) whether physical exercise in early life can prevent or delay cognitive decline in later life, (2) the effectiveness of exercise programs for individuals across the life span and for those with neurological diseases, and (3) how much exercise is necessary to gain beneficial effects on cognitive health. This is a field of research that deserves more attention.