Why should I elevate my legs after running?

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Ed asks: I saw cross-country runners lying on the ground after a practice with their feet propped up on a tree. Is there any merit to doing this?

That group of runners has learned either from their coach or from their own personal experience that the best way to prevent fainting after a hard run is to prop your legs up.

One of the causes of collapse following a distance run or race is exercise-associated postural hypotension. This is caused by the pooling of blood in the lower extremities as the leg muscle contraction associated with running stops squeezing the blood back to the heart. The blood vessels are dilated to maximise blood flow to the muscles during exercise, and the dilatation does not reverse as quickly as the blood flow. This can leave a runner with less blood flow to the brain, which can cause them to collapse.

“Legs up” is a common self-treatment and used to prevent exercise-associated collapse in medical tents around the world. There are other reasons for collapse like heat stroke, hyponatremia and cardiac arrest; fortunately these conditions are relatively rare.