How does physical activity affect the brain?

Physical activity has important benefits for both physical and mental health. Currently, anxiety and depression are the most prevalent mental disorders in the world. However, epidemiological studies have shown that physical exercise helps reduce these, in addition to being a good complementary therapy in the treatment of addictive behaviour and for reducing appetite and satiety.

Physical activity prevents age-related cognitive decline in healthy people, reduces the risk of developing dementia, can improve the quality of life in people with dementia, as well as the physical benefits that it brings. The WHO recommends taking regular physical exercise. A minimum of 150 minutes (2.5 hours) of physical activity per week, with more benefits obtained if you reach 300 minutes per week (5 hours).

Performing physical activity improves cognitive function, memory, efficiency and attention. One possible explanation is that it stimulates blood circulation in the neural circuits involved in cognitive function. The increase in cerebral blood flow releases more oxygen to the brain tissues, reduces muscle tension and increases blood at endocannabinoid receptors (involved in the sensation of appetite, sensitivity to pain, mood and memory). It also increases the production of serotonin, a neurotransmitter (brain molecule) related to the control of emotions and moods. An increase in this neurotransmitter, reduces anxiety and depression, psychotic behaviour and headaches. It also improves assertiveness, confidence, emotional stability, cognitive function, body image, self-control and sexual satisfaction.

What kind of exercise is good?

Aerobic physical activity or exercise requires oxygen to produce energy. Performing aerobic exercise at an intensity of 50-70% of the maximum heart rate (equivalent to moderate intensity) has beneficial effects for the brain. In practice, these are activities that require some effort to perform (and must be tiring) but without being strenuous. This obviously depends on one’s individual physical condition and features. Examples of aerobic exercise are fast walking, running, riding a bike on flat or slight inclines, light swimming and dancing at a good rhythm.

As well as the benefits derived from routine physical activity, benefits are observed when specific, individualised physical exercise or training programmes are followed. Positive effects in reducing anxiety and depression are found when specific physical training programmes are followed for at least 4 months.

Physical exercise and epigenetics

Epigenetics is the study of how genes interact with the environment and it has an essential role in neuroplasticity and memory processes. Environmental and biological factors and life habits can influence the activation of certain genes and affect the risk of developing certain diseases.

For example, there are RNA molecules called microRNAs (small RNA fragments found in cells and the blood) capable of inhibiting certain genes, and they are highly expressed in the brain. These molecules act as regulators of numerous processes in the central nervous system, such as cell proliferation, differentiation, apoptosis (cell death), synaptic plasticity and memory consolidation. Performing 4 weeks of physical exercise can induce epigenetic changes; that is, it can prevent the activation of genes related to the appearance of diseases.

Recent evidence suggests that physical exercise can mitigate the traumatic effects of brain injury and improve cognitive function in ageing, by regulating the expression of one of these molecules, called miR21.