It’s Not Just Endorphins—‘Hope Molecules’ Could Also Be Why You Feel So Good After Exercising

It is a fact that exercise makes you happy, and happy people just don’t shoot their husbands, they just don’t. (Well, by “fact,” we mean a fantastic legal argument from Elle Woods, but we digress…) But why does exercise have that happiness-inducing effect? Researchers are getting a better understanding of the answer to that question, and it could come down to a type of molecule called myokines.

Previously, endorphins have been the star of the show for the connection between exercise and mood: A good sweat session will cause a release of endorphins, which are neurochemicals produced in the pituitary gland that react with opiate receptors, meaning they make you feel really good. Working out also stimulates the production of serotonin and norphenylephrine, which are other happiness, wellbeing, and pleasure-inducing neurotransmitters.

These mood-boosting stimulations would probably be enough to give you that post-yoga glow. But there’s something even more going on.

Researchers have come to understand that when our muscles contract, they produce substances that get dispersed throughout the body. Some of these are chains of amino acids called myokines, and they are able to cross the blood-brain barrier—which means they can act on your brain. And when they get there, they improve brain function.

“Several myokines—irisin, hydroxybutyrate, etc.—have been shown to stimulate neuronal function and facilitate synapses, which are the way neurons communicate with each other,” Mychael Vinicius Lourenco, PhD, an assistant professor of neuroscience at the Federal University of Rio de Janeiro, who co-authored a recent review of research around myokines and brain function, previously told Well+Good.

That includes potentially “mediating the beneficial actions of physical exercise in the brain,” Lourenco and his co-authors write in the review. As a potential example, assisting with neuron communication could mean that myokines are helping those feel-good messages being sent by endorphins, serotonin, and norphenylephrine be heard.

Beyond just helping your brain do its job better, researchers also think that myokines could actually be a bulwark against depression. This has led to the substances garnering the name “hope molecules.”

In 2016, physical therapy and psychiatry researchers writing in the journal Physical Therapy were reviewing research on the connection between exercise and depression. They referenced a 2014 study on mice in which mice with lower levels of a certain type of myokine exhibit less resilience under stress than those mice with higher levels of the myokine.

“After a significant amount of stress, the mice appeared to ‘lose hope,’ as evidenced by their decreased survival efforts during forced swimming (an indicator of depression),” the authors write. “Altogether, these results suggest that the release of ‘hope molecules’ from the skeletal muscles of rodents influence mood disorder symptoms.”

While we can’t necessarily extrapolate the findings from studies on mice to humans, both species share some underlying biology that might cause myokines to work in a similar way. Namely, these myokines could inhibit a neurotransmitter pathway that, when it’s overactive, is linked with depression.

This was compelling enough for Stanford University psychologist Kelly McGonigal, the author of The Joy of Movement, to take notice of the study, and popularize the term. “Hope molecules,” McGonigal previously said on the Rich Roll podcast, could be like “an intravenous dose of hope.”

“It’s not just an endorphin rush,” McGonigal says on the podcast. “You go for a walk or a run or you lift weights and your muscles contract and they secrete these proteins into your bloodstream. They travel to your brain, they cross the blood-brain barrier. And in your brain, they can act as an antidepressant. Like irisin [a myokine] can make your brain more resilient to stress. They increase motivation. They help you learn from experience. And the only way you get these chemicals is by using your muscles.”

Even if research is still developing for how exactly exercise boosts mood and mental health, the link between exercise and wellbeing has never been clearer. Two recent meta-analyses on the effects of exercise in adults and exercise in kids have found it to be an effective bulwark against depression.

What with our emerging understanding of myokines, and the undeniable benefits of exercise, there’s never been a more compelling reason to take your medicine: A dose of movement.