I read this article on the BBC website and thought it might be interesting to those who like running. The full article can be found at: http://www.bbc.com/future/story/20151001-why-pain-feels-good
“The relationship will come as no surprise to those who run. Bursts of intense exertion release lactic acid, a by-product of the breakdown of glucose when oxygen is in short supply. The acid irritates pain receptors in the muscles, and these communicate their plight to the brain through electrical messages, sent through the spinal cord. The signals are interpreted as a burning sensation in the legs, usually causing the runner to slow down or stop.”
That is until the nervous system’s control centre, the hippocampus, kicks in. This seahorse-shaped portion of the brain responds to pain signals by ordering the production of the body’s own narcotics, endorphins. The proteins bind to opioid receptors in the brain and prevent the release of chemicals involved in the transmission of pain signals. This helps block pain, but endorphins go further, stimulating the brain’s limbic and prefrontal regions – the same areas activated by passionate love affairs and music. It’s a post-pain rush similar to the high of morphine or heroin, which also bind to the brain’s opioid receptors.
Meanwhile, the pain of intense exercise also causes a spike in another of the body’s painkillers, anandamide. Known as the ‘bliss chemical’, it binds to cannabinoid receptors in the brain to block pain signals and induce the warm, fuzzy pleasure emulated by marijuana, which binds to the same receptors. Adrenaline, also produced in response to pain, adds to the excitement by raising the athlete’s heart rate.
Burning legs are thought to discourage overexertion, while the ‘runner’s high’ may have enabled our ancestors to endure the pain of a marathon hunt. More generally, the pleasurable post-pain rush is thought to have evolved to help people cope in the immediate aftermath of an injury.”