The Crucial System Responsible For Runner’s High

couple running

Catherine O’Brien

A runner’s high is a state or feeling that is reached after a long bout of aerobic exercise. This state is often described as containing three distinct qualities:

  1. Euphoria

  2. Reduced anxiety

  3. Decreased sensitivity to pain

runner jumpingWhile this euphoric state is often equated with running, other types of aerobic exercise may produce these same effects. Not surprisingly, many people associate the runner’s high with endorphins. Continuous aerobic exercise does indeed increase levels of endorphins but there are other chemicals involved in producing this chill, blissful state.

Fortunately, in the last few years, research has started investigating the chemical cause of the runner’s high and such investigation has brought to light some interesting findings.

The Research

Research done by Fuss, Steinle, Bindila, Auer, Kirchherr, Lutz and Gass investigated the chemical components of the runner’s high in mice. The aim of their research is to show that cannabinoid receptors act as mediators in producing the euphoria, reducing the anxiety and diminishing pain sensitivity.

Why can’t we give endorphins all the credit? Fuss and colleagues point out that β- endorphin cannot cross the blood brain barrier. This means that, endorphins alone could not be causing the runner’s high response because they do not pass from the blood stream to the brain.  Enter endocannabinoids. The endocannabinoid system is an “important biological regulatory system” and is also important for immunoregulation, controlling motor functions, cognition, emotional responses, homeostasis and motivation (Nagarkatti et al. 2009, p.2). Fuss and colleagues were interested in demonstrating the role of endocannabinoids in the runner’s high response.

Related Article: Endocannabinoids: The Secret To Why Exercise Makes Us Feel Good

The Study

In order to test their theory, they conducted a series studies with mice. The first part of the study was a behavioral measure of the mice’s wheel running. All mice were exposed to a wheel for 3 days and then the wheel was removed for 2 days. Mice were then randomly divided into either a running condition or a control condition. In the running condition, the mice had access to the wheel for 5 hours a day while mice in the control condition were not given access to a wheel.

Dark-light Box Test

After the intervention, they measured levels of anxiety and sensitivity to pain. In order to test the mice’s levels of anxiety, they administered the dark-light box test. The dark-light box test includes two boxes, one that is dark with a lid and the other which is very bright with no lid. The amount of time the mouse spends in the aversive bright light area is indicative of their level of anxiety such that more time in the bright light indicates less anxiety. The amount of time it takes mice to exit the dark box, reach the light box and the amount of time spent in the light box were all measured for 5 minutes. Next, pain responses were measured using a hot plate. Pain response was indicated by licking hind legs or jumping. After the anxiety and pain responses tests, all mice were given access to the wheel for 1 hour.

The Findings

Mice in the running condition demonstrated lesser anxiety and lesser pain responses compared to the control mice. Mice in the run condition also ran less on the wheel that was presented at the end which indicated greater sedation compared to control mice.

Taking It A Step Further

In order to understand the role of endocannabinoids in the runner’s high state, the researchers repeated the same experiment but the second time around, injected the mice with either CB1 antagonist, CB2 antagonists (CB1 and CB2 are two prominent endocannabinoids), an endorphin antagonist naloxone, or a saline solution.

Similar to the first study, they found that the mice in the running condition demonstrated reduced anxiety. Interestingly, however, when the central cannabinoid receptor 1 (CB1) was inhibited, this anxiety reducing effect was not present. Regardless of drug administration, all other running mice experienced a reduction in anxiety. Pain sensitivity was shown to be mediated by peripheral CB1 and CB2 receptors. Mice in the running condition that had inhibited peripheral CB1 and CB2 receptors did not experience the same lessened pain response compared to other running mice.

Related Article: Think Positive Thoughts For A Better Workout

So What?

This study is exciting because it demonstrates the crucial role that endocannabinoids play in the runner’s high experience. While endorphins are often given the credit this study showed that the euphoric experience that is a runner’s high would not be possible if CB1 and CB2 were inhibited. The two studies conducted also demonstrated the real effects of aerobic exercise in producing a runner’s high. The present study utilized mice and wheel running but the findings can be extrapolated to other populations and exercises. Extended periods of exercise have the ability to create a “high” comprised of euphoria, reduced anxiety and decreased sensitivity to pain.

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Fuss, J., Steinle, J., Bindila, L., Auer, M.K., Kirchherr, H., Lutz, B., and Gass, P. (2015) A runner’s high depends on cannabinoid receptors in mice. Proceedings of the National Academy of Sciences, 112 (42), 13105-13108.

Nagarkatti, P., Pandey, R., Reider, S.A., Hegde, V. L., and Nagarkatti, M. (2009) Cannabinoids as novel anti-inflammatory drugs. Future Med Chem, 1(7), 1333-1349.

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