Endorphin release induced by exercise is the subject of a recent study conducted by researchers at Turku PET Centre, University of Turku. High-intensity interval training (HIIT) was found to increase the the release of endorphins and other opioid peptides in the brain areas controlling pain and emotions, butinduced negative feelings in the test subjects. The researchers compared these results to those of subjects who engaged in one-hour of aerobic exercise. The aerobic exercise did not induce significant release of endorphins, but nonetheless increased pleasurable feelings and euphoria which correlated with endorphin release. The research highlight that exercise intensity affects endorphin release and that the brain opioid system is involved in both positive and negative feelings caused by physical exercise performed at different intensities.