It is well-established that, while running, the body’s stress response is activated: the hypothalamic-pituitary-adrenal (HPA) axis¹. But how can it be then, that the runner isn’t constantly stressed while he has to deal with elevated levels of cortisol, the body’s main stress hormone?

This is particularly puzzling knowing that anxiety disorders and depression are characterized by stress response activation as well².

So, what happens to the runner’s body?

As the runner goes about his business, levels of stress hormones rise, and stay elevated for at least two hours after the run. On a rest day, the runner’s cortisol levels are similar to the couch potato’s³.

There are indications that running improves health⁴, memory and concentration⁵. This is due to a chemical responsible for neuronal growth, called brain-derived neurotrophic factor (BDNF). Running boosts release of this substance in two important areas: the frontal cortex (responsible for cognitive functions) and the hippocampus (essential in memory processes)⁵. However, the effects of stress are exactly opposite. What’s going on?

The brain adapts

The runner has a greater amount of stress hormone inactivation overnight, and this inactivation adapts to the amount of exercise⁶. So, doubling the amount of running in a week doubles the amount cortisol inactivation during the nights.

In addition, the pituitary becomes less sensitive to the stress hormones³. This is like when you start using a new deodorant: at first you are very aware of the smell, but as you use it more often, you hardly notice it.

The brain is high

Forget the oft-mentioned endorphin explanation of the “runner’s high’⁷ . Essential to our solution are endocannabinoids—yes, the brain’s self-produced cannabis. Going for a good run apparently boosts the release of these cool chemicals, which not only make you feel pleasant, relaxed, and increase your pain tolerance, they also tell the frontal cortex to stop fussing, and so dampen the stress response⁸!

What’s more, depression and anxiety disorders are related to lower levels of these endocannabinoids⁹. Exercise benefits not only clinical populations, but also healthy people: it decreases hormonal and heart rate response to stress¹⁰.

So, how do I run away from my troubles?

There is only a relative answer: run quite far, but not too far. Similarly, run quite hard, but not too hard. Running at 70-85% of your capacity (based on maximum heart rate) boosts your brain-cannabis the most, and so reduces stress the most.

More information:

1. Duclos, M. Corcuff, J. B., Arsac, L., Moreau-Gaudry, F., Rashedi, M., Roger, P., Tabarin, A., and Manier, G. (1998). Corticotroph axis sensitivity after exercise in endurance-trained athletes. Clinical Endocrinology, 48, 493-501.

2. Staufenbiel, S. M., Penninx, B. W. J. H., Spijker, A. T., Elzinga, B. M., and Van Rossum, E. F. C. (2013). Hair cortisol, stress exposure, and mental health in humans: A systematic review. Psychoneuroendocrinology, 38, 1220-1235.

3. Duclos, M., Corcuff, J. B., Pehourcq, F., and Tabarin, A. (2001). Decreased pituitary sensitivity to glucocorticoids in endurance-trained men. European Journal of Endocrinology, 144, 363-368.

4. Archer, T., Fredriksson, A., Schütz, E., and Kostrzewa, R., M. (2011). Influence of physical exercise on neuroimmunological functioning and health: aging and stress. Neurotoxic Research, 20, 69-83.

5. Tantimonaco, M., Ceci, R., Sabatini, S., Catani, M. V., Rossi, A., Gasperi, V., & Maccarrone, M. (2014). Physical activity and the endocannabinoid system: an overview. Cellular and Molecular Life Sciences, 71(14), 2681-2698.

6. Gouarné, C., Groussard, C., Gratas-Delamarche, A., Delamarche, P., Duclos, M. (2005). Overnight urinary cortisol and cortisone add insights into adaptation to training. Medicine & Science in Sports & Exercise, 37, 1157-1167.

7. Kolata G. Runner’s high? Endorphins? Fiction say some scientists. NY Times 2002, May 21.

8. Raichlen, D. A., Foster, A. D., Seillier, A., Giuffrida, A., and Gerdeman, G. L. (2013). Exercise-induced endocannabinoid signaling is modulated by intensity. European Journal of Applied Physiology, 113, 869-875.

9. Marco, E. M., García-Gutiérrez, M. S., Bermúdez-Silva, F. J., Moreira, F. A., Guimarães, F., Manzanares, J., and Viveros, M. P. (2011). Endocannabinoid system and psychiatry: in search of a neurobiological basis for detrimental and potential therapeutic effects. Frontiers in Behavioral Neuroscience, 5: 63.

10. Klaperski, S., Von Dawans, B., Heinrichs, M., and Fuchs, R. (2014). Effects of a 12-week endurance training program on the physiological response to psychosocial stress in men: a randomized controlled trial. Journal of Behavioral Medicine, 37, 1118-1133.