A sedentary person who starts a sports activity, begins to generate new connections between the small vessels (anastomosis) in his arterial and venous system, this means that the vascular structure is modified, becoming more efficient, because the tissues need more oxygen (among other things ) for the new requirement. When performing physical exercise, the function is "modified" and the structure is changed (new blood vessels, more powerful muscles, etc.). We already analyzed this in the entry of “The second law of osteopathy: the structure governs the function”. On this occasion we will only talk about vascular processes, which basically (and simplifying them) would be two: - Angiogenesis: is the process that consists of the formation of new blood vessels from pre-existing vessels. - Arteriogenesis: an increase in the diameter of existing arterial vessels. This means that our cardiovascular system adapts to these new demands, improving our ability to carry blood and fluids to the tissues. This in turn produces an effect that has been known since 1956 (it was studied in the arteries of the heart), called collateral circulation ("natural bridges" between blood vessels). These scientific studies have proven that aerobic training (walking, cycling, running, swimming, etc.) can promote this process and reduce the chances of angina pectoris or myocardial infarction occurring. A study presented at the American Heart Association International Conference on Stroke showed, in mice, that regular physical activity can prevent a CVA (cerebrovascular accident) or reduce its sequelae, thanks to the strengthening of collateral circulation in the brain.