Marathons are tough. Athletes push their bodies for miles and deal with cramping, dehydration and every runner’s worst fear: that extreme form of fatigue called “hitting the wall.â€� Why is distance running so difficult? With the New York City Marathon kicking off this Sunday,ÌýReactionsÌýruns through the science of distance running: why muscles burn, how sweat cools the body and the chemistry of runner’s high.
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