Active Voice: Endocannabinoids and Feeling Differently Post-Exercise — Uncovering Relationships in Depressed Women
By Jacob D. Meyer, Ph.D., and Kevin M. Crombie, M.S.

By Jacob D. Meyer, Ph.D.Kevin M. Crombie, M.S.

It’s a common phenomenon: After walking, jogging or running, people typically report mood improvements for minutes-to-hours after the exercise has ended. Although popular culture has ascribed this “feel-good” effect of exercise to endorphins, studies that experimentally blocked endorphins from binding to their receptors have led to mixed results. Some still showed mood improvements, even when endorphins were blocked. Despite considerable research examining endorphins and other neuromolecular systems, the mechanisms responsible for positive feelings following exercise remain largely unknown. Recent research suggests that a neuromodulatory system known as the endocannabinoid (eCB) system may play a significant role.

The eCB system, discovered in the early 1990s, consists of endogenous molecules known as endocannabinoids (eCBs) and cannabinoid receptors located in the brain and throughout the body. The eCB system’s nomenclature came from the Cannabis sativa plant (i.e., marijuana) because research into its main psychoactive component (?9-tetrahydrocannabinol) led to the discovery of the centrally located cannabinoid receptor. That, in turn, led to the discovery of the body’s own molecules that bind to these receptors (e.g., eCBs). The eCB system can halt the release of various neurotransmitters (e.g., glutamate, serotonin), and may play a role in clinical mental health disorders. For instance, individuals suffering from depression may have a dysregulated eCB system (e.g., lower levels of eCBs). In addition, recent research shows that an acute bout of exercise can increase eCBs and improve mood in healthy adults (Brellenthin et al., 2017) and adults with PTSD (Crombie et al., 2018). Together, the previous research led us to speculate that adults suffering from depression may feel better after exercising due to exercise-induced activation of the eCB system.

In our study, published in the September 2019 issue of Medicine & Science in Sports & Exercise®, we examined acute changes in eCB and mood states in women with major depressive disorder. In separate sessions one week apart, subjects (n=17) completed a prescribed, moderate-intensity cycling exercise session and a cycling session without intensity restrictions (i.e., self-selected/preferred session). The order of participation in the sessions was randomized and counterbalanced. Serum samples were taken before and within 10 minutes after exercise and analyzed for eCB content. Mood states were self-reported before as well as 10 minutes and 30 minutes post-exercise with the Profile of Mood States and State-Trait Anxiety Inventory (state only).

Our findings indicated relationships between elevations in eCBs with reductions in several negative mood states (i.e., depression, confusion, fatigue, state anxiety, total mood disturbance) up to 30 minutes following the moderate session. However, this was not the case for the self-selected/preferred session—even though the two sessions resulted in approximately equal improvements in mood. There are likely multiple pathways that translate exercise into positive mood responses, although these results suggest influencing the eCB system may be one important path.

While these results are of relevance to the general population, there is clinical interest in understanding how exercise improves mood states in people suffering from mood disorders. Understanding how mood states may be influenced by exercise can clarify what systems are involved in persistent low or abnormal mood, and how exercise training and other therapies might be able to target those systems to treat mood concerns. While preliminary, the present findings suggest further investigation into the eCB system during exercise is warranted. Ultimately, such work may lead to better understanding of how exercise can be used to improve mental health and wellbeing.

About the authors:
Jacob D. Meyer, Ph.D., is an assistant professor in the department of kinesiology at Iowa State University, moving there in 2017 after completing a postdoctoral research fellowship in the department of family medicine and community health at the University of Wisconsin-Madison. He earned his Ph.D. in kinesiology from UW-Madison, where his training focused on understanding the psychobiological effects of exercise in clinical populations. He is an ACSM member and involved in ACSM’s Psychobiology and Behavior Special Interest Group.

Kevin M. Crombie, M.S., is an ACSM member and doctoral candidate studying exercise psychology in the department of kinesiology at the University of Wisconsin-Madison. He is funded through a Ruth L. Kirschstein National Research Service Award Predoctoral Fellowship from the National Institute of Mental Health. His research focuses on delineating the role of exercise as part of a comprehensive treatment approach for adults with PTSD, possibly due to exercise-induced adaptations to the endocannabinoid system.

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