Researchers link the euphoric phenomenon that many experience after intense exercise to endocannabinoids. Photo Credit: Pixabay.
A runner’s high, as Dr. David Linden, professor of neuroscience at Johns Hopkins University School of Medicine explains, is “a short-lasting deeply euphoric state following intense exercise.”
Researchers have previously linked this euphoric state to the release of endorphins, the hormones that humans and animals produce as a result of pain or stress after exercise.
Linden explained in a research article that it is unlikely that these endorphins are responsible for euphoric feelings that many associate with a runner’s high, or any mood changes. As research suggests, the reasoning for this is that these hormones do not pass the blood-brain barrier in the body. But, biochemical substances known as endocannabinoids do.
However, as Dr. Hilary Marusak, assistant professor of psychiatry and behavioral neurosciences at Wayne State University in Michigan suggests, new research has found that endocannabinoids may be responsible for this phenomenon.
What are Endocannabinoids and What do They do?
Endocannabinoids are chemicals the body produces that are similar to those in cannabis, according to Linden. These chemicals are made of lipids – or fats – that bind to cannabinoid receptors within the brain and body.
Endocannabinoids are a part of a larger system — the endocannabinoid system (ECS). According to the Biological Psychiatry journal, an official journal of the Society of Biological Psychiatry, this system is “a widespread neuromodulatory system that plays important roles in central nervous system (CNS) development, synaptic plasticity, and the response to endogenous and environmental insults.”
In addition to endocannabinoids, this system consists of cannabinoid receptors and the enzymes that synthesize and degrade these chemicals, the journal reports.
Marusak helped conduct research that in the Cannabis and Cannabinoid Research journal. The study determined the ECS is critical in maintaining homeostasis, specifically in regulating metabolism and stress responses.
As Marusak notes in an interview with Salon, endocannabinoids can help relieve pain, anxiety and stress, and improve learning and memory. They can also impact hunger, inflammation, and immune functioning within the body. Food, time of day, exercise, obesity, injury, inflammation and stress can affect how many endocannabinoids are in the body.
“I like to think of them as a break,” Marusak explains to Emerald. “So, if you’re super stressed, your brain is basically having a stress response, and your endocannabinoids are produced within the brain whenever you’re stressed to help you tamp down that stress response.”
Endocannabinoids and the Runner’s High: More Movement = More Endocannabinoids
As Linden with the Johns Hopkins University School of Medicine noted in his research article, exercise increases the amount of endocannabinoids in the bloodstream. These chemicals move easily through the blood-brain barrier, which can induce temporary effects such as decreased anxiety and calm feelings that many associate with a runner’s high.
According to Marusak, research hypothesizes that exercise produces endocannabinoids from intense skeletal muscle movement. That movement disperses these chemicals into the blood, which the body then circulates to the brain.
Marusak further explains that, “endocannabinoids are lipids, so they’re little fat molecules and they love fatty brain tissue. It does make a whole lot of sense that they would be getting into the brain and working on the receptors, which are in a lot of brain areas that we know are really important for anxiety and stress responding.”
Interestingly, in another study, scientists found similar effects in mice after exercise as a result of increased endocannabinoid levels. The study observed mice after running on a wheel. Researchers found that the mice had higher endocannabinoid levels after exercise, and lower levels of anxiety and pain sensation.
The study also determined that reduced anxiety stems from cannabinoid 1 (CB1) receptors located in GABAergic neurons in the brain. These neurons produce the neurotransmitter and amino acid Gamma-aminobutyric acid (GABA. GABA serves as the primary inhibitory neurotransmitter for the central nervous system (CNS), research shows. Although, pain reduction was linked to the activation of both CB1 receptors and CB2 receptors in the peripheral nervous system.
Ultimately, scientists in the study also discovered that an intact ECS is necessary for a runner’s high in mice.
Can all Types of Exercise Cause a Runner’s High?
To answer this, Marusak’s student, Shreya Desai, led a systematic review of studies from the previous 20 years.
The research “compared the effects of an ‘acute’ exercise session – like going for a 30-minute run or cycle – with the effects of “chronic” programs, such as a ten-week running or weightlifting program,” according to the review.
Desai concluded that acute exercise was responsible for increased endocannabinoid levels. The effects of acute exercise came from an endocannabinoid called anandamide or the “bliss” molecule. Experts know this molecule for creating positive effects on mood.
Overall, Marusak tells Emerald that all acute exercise boosted endocannabinoid levels in the blood. However, some forms of exercise produced more endocannabinoids than others.
The researchers also compared different types of exercise to determine how they would impact endocannabinoid levels. They found that moderate levels of exercise intensity – such as cycling or running – raised endocannabinoid levels more than lower-intensity methods – like walking at slow speeds or low inclines.
The review also suggested the importance of keeping one’s heart rate elevated during exercise. Marusak notes that any form of exercise that gets a heart rate up seems to boost endocannabinoid levels better than those associated with a lower heart rate.
Marusak says there are still unanswered questions. For example, how long should one exercise to boost endocannabinoid levels? How long do endocannabinoid levels remain elevated after exercise?
“We couldn’t tell if 30 minutes is better than an hour. We don’t really know how long endocannabinoids remain elevated after exercise,” she said. “Those are all things we need to answer with more studies.”
While research has answered many questions about endocannabinoids and their impact on the runner’s high; there is still more work to be done to understand these chemical’s effects, Marusak emphasizes.