The network of blood vessels (collateral circulation) shrinks in number and diameter as the brain ages. Collateral circulation allows blood flow to be rerouted when arteries narrow. Using mice, researchers found that this loss of collateral vessels is prevented by exercise, according to a study presented at the American Heart Association’s International Stroke Conference 2017.

Source: Regular aerobic exercise beginning in middle age may lessen severity of stroke in old age — ScienceDaily

….