A recent study by the University of Turku's Positron Emission Tomography (PET) centre has found that high-intensity interval training (HIIT) results in increased endorphin release in the brain, which may play a role in mitigating physical and emotional stress caused by high-intensity exercise.

Comparing moderate and high-intensity exercise, researchers identified that HIIT significantly increased the release of endorphins and other opioid peptides in the brain areas controlling pain and emotion.

A less demanding one-hour aerobic exercise did not cause similar endorphin release.

However, such moderate exercise did result in pleasurable feelings and euphoria, which are linked to endorphin release.

Researchers involved in the study found that at high intensities of exercise, the release of endorphins appears to be linked to increased negative feelings and pain, which may be required to manage the physically and emotionally demanding challenge.

The Turku team think that this exercise-induced endorphin release might determine whether we maintain motivation during exercise, pushing ourselves to continue working out despite physical and emotional pain or exhaustion.

To carry out the study, participants were injected with a radioactive compound that binds to their brain's opioid receptors.

Radioactivity in the brain was measured with the PET scanner in three conditions: after a 60-min aerobic moderate-intensity exercise session, after a HIIT session and finally while resting.