Although many people in the scientific community dispute the idea of endorphins (or anything else) causing a "high" in runners, I don't know one serious runner who hasn't experienced this feeling. What is it about running, especially really hard or long, that causes us to feel that euphoric, relaxed high? A recent study was conducted, which for the first time showed increased levels of endorphins in certain areas of the brain after a two hour jog. Scientists are beginning to realize that there is more to the endorphin theory than just myth. (Boecker, 2008)
Endorphins are neurotransmitters released in the brain after experiencing a significant amount of pain and they calm physical (and some believe psychological) pain. Endorphins are a human's natural opiate, like morphine, which is released to numb pain. (Boecker, 2008) In my experience with running, I feel amazing directly after a mental battle of whether or not I should turn in my running shoes forever. This point in my run usually only comes after a real significant time of running and I really feel that it is due to some type of chemical release in the brain. However, I am just one person and cannot make assumptions saying that this is the point of endorphin release (but it sure does seem like that).
So, the idea now is to find out, not only if the added release of endorphins are the cause of the "runner's high" feelings, as it has also been shown that exercise can release the neurotransmitters serotonin and dopamine. Serotonin is a neurotransmitter related to mood and dopamine is related to arousal. Since these two neurotransmitters can be linked to "feel good" emotions and dopamine can cause the relaxation, perhaps it is a combination of all three fun little neurotransmitters which give us a runner's high. Raised serotonin levels improve mood and relieves anxiety; raised dopamine levels cause relaxation while prolonging energy set specifically for running; raised endorphin levels numb the pain (or the perception of pain, really). Sounds like an awesome combination to me!
Boecker, Henning. (2008). Brain imaging explores the myth of runner's high. Medical News
Today. Retrieved February 15, 2009, from http://www.medicalnewstoday.com/articles/99420.php.