You’ve probably felt it: at the end of an intense run, you start to experience mild dizziness or light-headedness. You may have even fainted after a particularly difficult race. These are symptoms of a phenomenon known as exercise-associated postural hypotension, a technical way of describing a lack of blood flow to your brain following intense exercise. But what exactly is happening inside your body that causes this, and how can elevating your legs above your head help prevent it?
During long and intense runs, such as endurance races, your body maximizes blood flow to your extremities to feed muscles the oxygen they need for fuel. The continuous contraction of your muscles acts as a pump, helping your body circulate blood to your legs and back to the heart. Blood vessels also expand, or dilate, in order to increase the volume of blood that can reach your muscles.
Once you stop that continuous movement, however, these adjustments in your body’s circulatory system begin to work against you. Your body is now accustomed to your legs providing some needed pumping power, and it takes time for the veins that had previously dilated to return to their normal size. Combine the reduced leg muscle contraction with expanded veins, and you get blood pooling in your lower legs, leaving the brain starved for oxygen. This is where the dizziness comes from, and in some cases, Exercise-Associated Collapse (EAC).
One way to stop EAC from happening to you after your race is to lie down and lift your legs above your head, allowing gravity to give you a much needed assist. The laws of physics say that the greater the depth of a fluid, the greater the pressure. This means the higher you keep your legs after your run, the greater the flow of blood is back to your brain.
Another way to keep yourself from experiencing faintness after your run is to wear compression socks or calf sleeves, as these assist your body in much the same way your leg muscles do when you run. The difference, of course, is that even when your leg muscles stop pumping the compression sleeves do not! The pooling of blood in your legs happens after every run, to varying degrees, and compression apparel is one of the most effective solutions in avoiding that dizzy feeling.
Something to note: if you ever feel dizzy or faint during your run, or collapse, putting your legs above your head will not necessarily help, as this can be a sign of a more serious cardiovascular or other medical issue.
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