One of the most captivating aspects of regular physical activity, especially running, is the euphoric feeling of accomplishment and exhilaration experienced post-workout, often referred to as the "runner's high". Despite its name, this phenomenon isn't exclusive to runners; it can be elicited by any form of sustained, vigorous exercise. But what's the biology behind this phenomenon? Let's lace up our metaphorical running shoes and dive into the world of endorphins and exercise.
The term "runner's high" was first coined in the 1970s to describe the "feel-good" sensation that seems to envelop runners after a certain period of vigorous and sustained physical activity. For many, it's characterized by a sense of euphoria, a surge of energy, and a decreased perception of pain or discomfort.
In the quest to decipher the biology behind this feeling, early research led scientists to a group of chemicals produced in the brain, known as endorphins (1). These molecules, structurally similar to morphine, are part of the body's natural pain-relief system. The word "endorphin" is actually derived from "endogenous", meaning originating within the body, and "morphine", a powerful painkiller.
During sustained exercise, the body experiences physical stress, and in response, it begins to produce endorphins to help cope with this stress. These chemicals are released from the pituitary gland into the bloodstream and can cross the blood-brain barrier. They then bind to opioid receptors in the brain, reducing the sensation of pain and potentially inducing feelings of euphoria, thus leading to the so-called "runner's high" (2).
However, the endorphin hypothesis has recently been challenged. It's been noted that the euphoria associated with the runner's high occurs more frequently in endurance or aerobic exercises such as running or cycling, which are performed over an extended period. This observation led researchers to hypothesize that there might be other factors at play. Enter endocannabinoids - chemicals that are structurally similar to the active compound in cannabis (THC). Endocannabinoids can also cross the blood-brain barrier and bind to the same receptors as THC, leading to feelings of pleasure and euphoria (3).
A breakthrough study published in 2015 used mice to show that after running, the level of endocannabinoids in the bloodstream increased. Moreover, when they used drugs to block the endocannabinoid system, the mice didn't exhibit the usual post-run anxiety reduction, suggesting endocannabinoids may play a key role in inducing the runner's high (4).
Both endorphins and endocannabinoids released during exercise can contribute to a positive mood post-workout. However, it's crucial to note that the runner's high isn't guaranteed every time you lace up your sneakers. The intensity and duration of the workout, your fitness level, and even your mindset can influence whether you experience this phenomenon.
While scientists are still piecing together the intricate neurochemical puzzle behind the runner's high, one thing is clear: regular exercise offers profound benefits for both physical and mental health. Whether you're an avid runner or prefer other forms of vigorous physical activity, chasing that "high" can be a great motivator to keep moving. The runner's high represents the body's natural reward system for physical exertion, a testament to the age-old adage that what's good for the heart is good for the mind.
References:
Goldfarb, A. H., & Jamurtas, A. Z. (1997). Beta-endorphin response to exercise. Sports Medicine, 24(1), 8-16.
Boecker, H., Sprenger, T., Spilker, M. E., Henriksen, G., Koppenhoefer, M., Wagner, K. J., ... & Tolle, T. R. (2008). The runner’s high: opioidergic mechanisms in the human brain. Cerebral Cortex, 18(11), 2523-2531.
Raichlen, D. A., Foster, A. D., Seillier, A., Giuffrida, A., & Gerdeman, G. L. (2013). Exercise-induced endocannabinoid signaling is modulated by intensity. European journal of applied physiology, 113(4), 869-875.
Fuss, J., Steinle, J., Bindila, L., Auer, M. K., Kirchherr, H., Lutz, B., & Gass, P. (2015). A runner’s high depends on cannabinoid receptors in mice. Proceedings of the National Academy of Sciences, 112(42), 13105-13108.