There are many reasons you exercise, but none is more enticing than the buzzy bliss that comes from a satisfying sweat session. After all, mood-boosting endorphins — aka your body’s built-in pain killers — are one of the main sells of long runs. But is the so-called runner’s high exclusive just to running?
While most forms of exercise will release endorphins, the path to happy will differ. According to recent research published in Neuropsychopharmacology, the flow of these feel-good molecules depends on exercise intensity and plays a unique role in how we perceive our workouts.
A HIIT of Endorphins
Researchers at the University of Turku in Finland studied the effects of different types of exercise on endorphin release and mood. As your body’s natural opioid, endorphins are neurotransmitters that activate your brain’s reward system and minimize pain.
Participants of the study underwent three position emission tomography (PET) scans to illustrate brain functioning before and after exercise. They did one at rest, one after an hour of moderate-intensity exercise and another one after a high-intensity interval training (HIIT) session. What they found was that HIIT significantly increased the flow of endorphins in the brain, particularly to the areas that control pain and emotions. But interestingly, moderate-intensity aerobic session didn’t.
Tina Saanijoki, one of the researchers of the study, says, this is one of the first studies of its kind. “No studies have compared opioid release after moderate and high-intensity exercise at the brain level.” She says, “The finding that HIIT led to opioid release didn’t surprise us, but we were somewhat surprised that in the group level, we didn’t observe opioid release after one-hour of aerobic exercise.”
Runner’s High: Is It All in Your Head?
Surprisingly, researchers discovered that the moderate-intensity aerobic work left participants feeling euphoric, even though there wasn’t a flood of the neurochemicals in the brain. Which begs the question: Is runner’s high all in our heads? Saanijoki says, “Runner’s high is a subjective experience, and we don’t have a scientific determination, criteria or a measure for it.” So if you don’t get that glowing feeling post-10K, you’re not alone. “The description of runner’s high varies considerably between people who have experienced it, and even then, they don’t get there every time,” she explains.
Meanwhile, while the HIIT participants showed a measurable endorphin rush, they experienced a rush of negative feelings, too. Participants reported exhaustion, irritation and lack of energy. Instead of the typical post-workout glow, the intense bout of exercise caused the exact opposite effect.
Understanding the Endorphin Rush
The findings suggest that endorphins can have a dual effect on your body and mind, depending on the intensity of your workout. “[Endorphins] appear to be involved in positive emotions at moderate intensities and in modulating negative emotions and perhaps pain at very high intensities,” Saanijoki says. “The opioid release after HIIT likely is the body’s protection response to this physically and emotionally stressful situation.” Which makes sense. Who hasn’t felt like keeling over after a killer AMRAP workout?
Since feeling like death post-workout isn’t everyone’s cup of tea, hit up a HIIT session with caution, especially if you’re just starting to exercise or struggling to keep up your gym habit. In that case, a moderate-intensity aerobic session may be a better fit. You may be more motivated to come back for the feel-good vibes that accompany those workouts.