When you exercise, increased activity in your muscles triggers an increased need for oxygen-rich blood. To meet this vital need, your heart rate speeds up and blood flow to your body increases. Blood flow to your brain also increases, although the extent of this increase may depend on the intensity of the exercises you perform.
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When you need extra oxygen during exercise, your breathing automatically deepens and your breathing rate increases. Deep within your lungs, this oxygen passes into your bloodstream through tiny blood vessels called capillaries. Oxygen-rich blood reaches your brain through your internal carotid arteries and your vertebral arteries. Inside your brain, your internal carotid arteries branch out and form two main additional arteries, called the middle and anterior cerebral arteries, which supply oxygen-bearing blood to the front of your brain.
When you exercise, the flow of blood through your internal carotid arteries and cerebral arteries increases by roughly 25 percent, according to a study reported in 2008 in the "Journal of Applied Physiology." This finding reverses earlier research, which measured the flow of blood leaving the brain and found no changes during exercise. However, if you exercise at very high intensity, the oxygen content of the blood flowing to your brain will eventually drop. In turn, this drop in your brain’s oxygen levels will reduce its ability to properly coordinate your muscles and will contribute to symptoms of exercise fatigue.
Walking is particularly good for your brain and increases blood flow, oxygen levels and your brain’s supply of a vital energy source called glucose, the Franklin Institute reports. When you perform more strenuous forms of exercise, increased oxygen and glucose needs in your muscles can decrease the amount of these substances your body can send to your brain. However, walking is gentle enough to provoke only modest increases in your muscles’ energy needs, leaving your brain with a more readily available fuel supply.
In addition to increasing short-term blood flow to your brain, regular exercise can help to improve and protect the higher functions of your brain — such as memory, task coordination, scheduling and planning — as you age. What’s more, according to a study conducted in 2006 by the University of Illinois at Urbana-Champaign and Amsterdam’s Vrije Universiteit, the brain-related benefits of exercise also seem to appear in younger adults, teenagers and children. While these findings are preliminary, they may point to a new, important rationale for engaging in regular exercise at an early age.