Endorphin

Endorphins are one of the body's own painkillers, an opioid (morphine-like) chemical produced by the body that serves to suppress pain.

Endorphins are manufactured in the brain, spinal cord, and many other parts of the body. They are released in response to neurotransmitters and bind to certain neuron receptors (the same ones that bind opiate medicines). Endorphins act as analgesics (diminishing the perception of pain) and as sedatives.

Endorphins are released during long, continuous workouts, when the level of intensity is between moderate and high, and breathing is difficult. This also corresponds with the time that muscles use up their stored glycogen. Workouts that are most likely to produce endorphins include running, swimming, cross-country skiing, long distance rowing, cycling, hockey, tennis, weight lifting, aerobics, or playing a sport such as soccer, basketball, rugby, or American football.