Final answer:
Endorphins are responsible for 'runner's high' during long-distance running or vigorous aerobic exercise.
Step-by-step explanation:
Endorphins, the neurotransmitters behind the euphoria of 'runner's high,' are vital in pain management. Produced by the pituitary gland and hypothalamus during intense aerobic activities like long-distance running, endorphins contribute to a positive emotional state. These natural chemicals act as the body's internal painkillers, elevating mood and creating a sense of well-being. The phenomenon of 'runner's high' highlights the remarkable impact of endorphins on our physiological and psychological responses to strenuous exercise, fostering a rewarding and enjoyable experience.