Many people have experienced a reduction in stress, pain and anxiety and sometimes even euphoria after exercise. What’s behind this so-called “runner’s high”? New research on the neuroscience of exercise may surprise you.
The “runner’s high” has long been attributed to endorphins. These are chemicals produced naturally in the bodies of humans and other animals after exercise and in response to pain or stress.
However, new research from my lab summarizes nearly two decades of work on this topic. We found that exercise reliably increases the body’s levels of endocannabinoids – which are molecules that work to maintain balance in the brain and body – a process called “homeostasis.” This natural chemical boost may better explain some of the beneficial effects of exercise on the brain and body.
I am a neuroscientist at Wayne State University School of Medicine. My lab studies brain development and mental health, and the role of the endocannabinoid system in stress regulation and anxiety disorders in children and adolescents.
This research has implications for anyone who exercises to reduce stress and should serve as motivation for those who do not exercise regularly.
Health Benefits of Exercise
Several decades of research have shown that exercise is beneficial to physical health. These studies find a consistent link between varying amounts of physical activity and a reduced risk of premature death and dozens of chronic health problems, including diabetes, hypertension, cancer and heart disease.
Plus récemment – au cours des deux dernières décennies environ – des recherches de plus en plus nombreuses montrent que l’exercice est également très bénéfique pour la santé mentale. En fait, l’exercice régulier est associé à une diminution des symptômes d’anxiété, de dépression, de la maladie de Parkinson et d’autres problèmes de santé mentale ou neurologiques courants. L’exercice régulier est également lié à de meilleures performances cognitives, à une meilleure humeur, à une diminution du stress et à une meilleure estime de soi.
On ne sait pas encore ce qui se cache derrière ces améliorations de la santé mentale. Nous savons que l’exercice a divers effets sur le cerveau, notamment en augmentant le métabolisme et le flux sanguin, en favorisant la formation de nouvelles cellules cérébrales – un processus appelé neurogenèse – et en augmentant la libération de plusieurs produits chimiques dans le cerveau.
Certains de ces produits chimiques sont appelés facteurs neurotrophiques, tels que le facteur neurotrophique dérivé du cerveau. Le BDNF est étroitement impliqué dans la « plasticité » cérébrale ou les changements dans l’activité des cellules cérébrales, y compris celles liées à l’apprentissage et à la mémoire.
Scientists have also shown that exercise increases blood levels of endorphins, one of the body’s natural opioids. Opioids are chemicals that act in the brain and have a variety of effects, including helping to relieve pain. Some early research in the 1980s contributed to the long-held popular belief that this release of endorphins is linked to the euphoric sensation known as the runner’s high.
However, scientists have long questioned the role of endorphins in the runner’s high, in part because endorphins cannot enter the brain through the blood-brain barrier, which protects the brain from toxins and pathogens. So endorphins are probably not the main driver of the beneficial effects of exercise on mood and mental state.
This is where our research and that of others points to the role of our body’s natural versions of cannabinoids, called endocannabinoids.
The surprising role of endocannabinoids
You may be familiar with cannabinoids such as tetrahydrocannabinol – better known as THC – the psychoactive compound in cannabis (from the plant Cannabis sativa L.) that makes people feel high. Or you may have heard of cannabidiol, commonly known as CBD, a cannabis extract infused into some foods, medicines, oils and many other products.
But many people don’t realize that humans also create their own versions of these chemicals, called endocannabinoids. These are tiny molecules made of lipids – or fats – that circulate in the brain and body; “endo” refers to those produced in the body rather than from a plant or in a lab.
Endocannabinoids act on cannabinoid receptors throughout the brain and body. They cause a variety of effects, including pain relief, reduced anxiety and stress, and improved learning and memory. They also affect hunger, inflammation and immune function. Endocannabinoid levels can be influenced by food, time of day, exercise, obesity, injury, inflammation and stress.
It should be noted that one should not be tempted to forgo a run or bike ride and instead resort to smoking or ingesting cannabis. Endocannabinoids do not have the side effects that come with getting high, such as mental impairment.
Understanding the runner’s high
Studies in humans and animal models indicate that endocannabinoids – not endorphins – are the star players in the runner’s high.
These elegant studies show that when opioid receptors are blocked – in one example by a drug called naltrexone – people still experience euphoria and reduced pain and anxiety after exercise. On the other hand, studies have shown that blocking the effects of cannabinoid receptors reduces the beneficial effects of exercise on euphoria, pain and anxiety.
While several studies have shown that exercise increases circulating levels of endocannabinoids in the blood, some have reported inconsistent results or that different endocannabinoids produce varying effects. We also don’t know if all types of exercise, such as cycling, running, or resistance exercise like weightlifting, produce similar results. And it’s an open question whether people with and without pre-existing health conditions like depression, PTSD or fibromyalgia experience the same endocannabinoid surges.
To answer these questions, an undergraduate student in my lab, Shreya Desai, conducted a systematic review and meta-analysis of 33 published studies on the impact of exercise on endocannabinoid levels. We compared the effects of an “acute” exercise session – such as a 30-minute run or cycle – with the effects of “chronic” programs, such as a 10-week running or weightlifting program. We separated them because different levels and patterns of exercise could have very distinct effects on endocannabinoid responses.
We found that intense exercise consistently increased endocannabinoid levels in all studies. The effects were most consistent for a chemical messenger known as anandamide – the so-called “happiness” molecule, which has been named, in part, for its positive effects on mood. Interestingly, we observed this exercise-related increase in endocannabinoids in different types of exercise, including running, swimming, and weightlifting, and in individuals with and without pre-existing health problems. Although only a few studies have examined the intensity and duration of exercise, it appears that moderate levels of exercise intensity – such as cycling or running – are more effective than low-intensity exercise – such as walking at a slow pace or with a low incline – when it comes to increasing endocannabinoid levels. This suggests that it’s important to keep your heart rate up – that is, between about 70% and 80% of your age-adjusted maximum heart rate – for at least 30 minutes to reap the full benefits.