Final answer:
Endorphins are the hormones released by the brain during exercise that help to reduce pain and are attributed to the 'runner's high.' They also play a role in exercise-induced changes in mood and can lead to exercise addiction.
Step-by-step explanation:
The group of hormones that are released by the brain during exercise, which help reduce pain, is endorphins. These hormones are known for their pain-relieving effects and are often associated with the feeling of a "runner's high." This euphoric sensation comes from the release of β-endorphin, which is thought to contribute to the reduction in anxiety and depression due to exercise.
While endorphins do play this role, recent studies suggest that a release of endocannabinoids could also be responsible for these feelings during exercise. Endorphins may even contribute to exercise addiction due to the need for more intense exercise to achieve the same endorphin rush, as the brain may downregulate their production during rest periods to maintain homeostasis.