Perhaps, you have felt, at the end of a great run, the sensation of relaxation bordering on euphoria. This phenomenon is commonly referred to as a runner's high. It can be experienced as a reduction in anxiety or even a higher tolerance for pain.
The weight of life that several miles ago seemed to be crashing down on you has been released. The aches and pains of your body are gone and you feel as if you drank the elixir of youth. This feeling is why many runners pound the pavement day in and day out. It is a sensation that those who do not engage in serious aerobic activity might go their entire lives without knowing.
What's more, each runner who has experienced it describes it differently from every other runner. There is no single, universal experience of runner's high, making the sensation all the more mysterious and intriguing.
For years, it was believed that runner's high was caused by the release of endorphins during exercise. A recent study, though, possibly refutes that theory. The group leading this project, Fuss et al, studied several sets of lab mice in an attempt to uncover the true reason that endurance athletes often feel a subjective "high" at the end of heavy exercise. After completing several tests, researchers determined that the endorphins produced by exercise did not affect the moods of the lab mice. The exercise did increase their levels of endocannabinoids, though, which left the mice feeling less anxious and reduced their ability to feel pain.
But what is an "endocannabinoid?" If you dive into the etymology, you may notice that it sounds familiar. That is because endocannabinoids are chemicals that are a part of the same system that is also affected by marijuana (cannabis). The ways people describe runner's high start to make sense when put in this context: a feeling of being lighter than air as all your worries float away.
The one caveat regarding this study is that the results don't necessarily prove that aerobic exercise has the same effect on humans as the mice that were tested, though it does open the door for further research on this topic.
Perhaps on those days when running feels like a chore and you can't think of a single reason to head out to exercise, remember that there is a tangible end goal worth working towards. Endocannabinoids could relax all your pain and anxiety if only you commit to putting one foot in front of the other at a steady pace. So, get out the door, let running be your drug and keep chasing that next runner's high.