**5. Conclusions**

In recent years, the research of human gut microbiota and their interaction with their human host has extensively increased. It has been shown that the composition of the gut microbiota is influenced by several factors such as diet, age, host genetics, drugs, as well as exercise and its level of activity. Animal and human studies have indicated that gut microbiota plays an important role in the occurrence of several diseases. Mainly, it has been evidenced that its composition and function have a direct effect on host physiology and can also affect physical performance.

Exercise improves the diversity of the gut microbiota, the maintenance of normal gut physiology, and contributes to the reduction of gastrointestinal symptoms and inflammatory markers in various pathological conditions as well as altering hundreds of metabolites.

Therefore, regular physical activity should be considered as a treatment to maintain the eubiosis of the microbiota, leading to an improvement in health status. Higher CRF levels lead to greater bacterial diversity, regardless of diet. Aerobic activities appear to be able to produce significant changes in the composition of the microbiota, although the modalities and intensity of exercise may affect the microbiota differently.

The amount and frequency recommended by WHO (the minimum dose of physical activity) for adults seem to cause some changes in the composition of the microbiota. Strenuous and/or excessively prolonged exercise with inadequate carbohydrate intake may have a negative impact on the microbiota due to inflammation and gastrointestinal symptoms. Nevertheless, further studies are needed to understand how physical activity and diet independently affect the microbiota.
