Endocannabinoids. For years, endorphins were thought to cause the infamous runner’s high, but it is now evident that endocannabinoids—the body’s natural version of marijuana’s active ingredient—play a much greater role in this phenomenon.24 Despite causing a truly pleasurable high, this system has little relevance for most exercisers because it usually takes several hours of vigorous physical activity before the brain releases these mood- and sensory-enhancing drugs. Further, not everyone has the genes that make a runner’s high possible.25 I suspect the runner’s high evolved primarily to
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