Runner's high

Please explain "runner's high" in this sentence: While the actual state that they feel varies immensely for each individual there is a common feeling associated with the term "runner's high".

My comments:

You need only get off your feet – to wit, run – to experience the runner's high.

Runner's high refers to the feeling of elation experienced by runners, especially while running long distance. To most people, me included, distance running is a daunting task. But lately, in order to work my injured knees back to full strength so that I can play competitive basketball again, I've been running the jogging machine. I can't call it running as I go at a speed of merely 5 kilometers per hour – most people walk at that pace as a matter of fact – but I do it landing on my toes only, keeping my back heels off the ground throughout the workout.

Anyways, the first few minutes feel like a chore. The legs are heavy and the joints are stiff but after about 15 minutes my feelings are different. Gone are any emotions of pain, burden or fatigue, and a feeling of light-heartedness begins to permeate my body. The limbs are light and effortless moving and I feel like remarking: Gee, I don't mind going on thus forever.

That's "runner's high" for me, and I've never taken to running all of my life. Now imagine what that feeling is like for, say, a marathon runner (who runs for fun rather than an Olympic medal). For them, the feeling is sometimes described as exhilaration, euphoria and ecstasy.

Scientifically speaking, runner's high is understood to be caused by what is called endorphins, which are "chemically similar to morphine, that the brain releases to relieve pain" (Womensheart.org).

And Wikepedia explains it in greater detail (you've got to look up the dictionary for all the medical terms):

Endorphins are endogenous opioid polypeptide compounds. They are produced by the pituitary gland and the hypothalamus in vertebrates during strenuous exercise, excitement, pain and orgasm, and they resemble the opiates in their abilities to produce analgesia and a sense of well-being. Endorphins work as "natural pain relievers", whose effects may be enhanced by other medications.

And this article, Exercise and Depression (Webmd.com), explains why "runner's high" is good for you:

Endorphins also trigger a positive feeling in the body, similar to that of morphine. For example, the feeling that follows a run or workout is often described as "euphoric." That feeling, known as a "runner's high," can be accompanied by a positive and energizing outlook on life.

Endorphins act as analgesics, which means they diminish the perception of pain. They also act as sedatives. They are manufactured in your brain, spinal cord, and many other parts of your body and are released in response to brain chemicals called neurotransmitters. The neuron receptors endorphins bind to are the same ones that bind some pain medicines. However, unlike with morphine, the activation of these receptors by the body's endorphins does not lead to addiction or dependence.

Regular exercise has been proven to help:

Reduce stress

Ward off anxiety and feelings of depression

Boost self-esteem

Improve sleep

Exercise also has these added health benefits:

It strengthens your heart.

It increases energy levels.

It lowers blood pressure.

It improves muscle tone and strength.

It strengthens and builds bones.

It helps reduce body fat.

It makes you look fit and healthy.