Opioid Release after High-Intensity Interval Training in Healthy Human Subjects

Neuropsychoparmacology


THE STUDY
22 active dudes were injected with a radioactive compound that binds to their brain's opioid receptors, which was then measured using positron emission tomography (PET). Sounds to me like the making of a sci-fi flick (Stranger Things 2 maybe??), but it worked so power to the scientists on that one.

The opioid receptors were measured in three conditions on separate days: after a 60-min. aerobic moderate-intensity exercise session, after a high-intensity interval training (HIIT) session, and after rest. Self-reported mood was also measured throughout the experiment.

WHY I CARE
There are days when I bike home after a long day and feel even more tired and more irritated then before I started. That said, there are also plenty of days when I get home from a ride feeling totally rejuvenated and fired up to make dinner with my wife and get a few more hours of studying in. Of course there are many variables that might change my emotions after exercise, but I'd love to know what causes the positive reactions.


RESULTS
HIIT released endorphins (can make you happy, decrease pain) but the participants also noted negative feelings (to be expected from a harder workout maybe?).

In addition, at moderate training intensities, participants noted pleasurable sensations, also likely caused by the release of endorphins, save the pain.

Which begs for the question, which level of intensity is preferable?


SCIENTIST SAYS...
"Our results 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," said Tiina Saanijoki from Turku PET Centre.

"At moderate training intensities, the pleasurable sensations caused by the possible release of endorphins may promote habitual exercise. At very high exercise intensities the release of endorphins appears to be linked to increased negative feelings and pain, and may be needed to manage the emotionally and physically demanding challenge. However, such negative feelings may discourage further exercise."


TAKEAWAY: Despite what a certain president has said, exercise is an ideal way to improve health. The trick is finding the motivation to do it on a regular basis, allowing for the most benefits. Exercise-induced endorphin release may be an important mechanism which supports exercise motivation and maintenance of regular exercise. HIIT, although very effective at building endurance and improving heart strength, may not be a sustaining form of exercise. Moderate exercise for an hour was shown to provide a positive mood boost without the physical pain. But hey, no pain no obtain (or something like that).