It is a familiar feeling for anyone who enjoys staying active: when acute stress hits, the motivation to go to the gym, step on a basketball court, or engage in any physical activity takes a hit, with motivation evaporating and stress condensing, clouding one’s mind. This phenomenon often feels like a psychological failure that one attributes to a lapse of their own self-discipline and inability to coordinate the different facets of life in a succinct fashion, but as our speaker Dr. Buhr highlighted a few weeks ago, it is actually a deeply ingrained biological response.
In his talk, Dr. Buhr explored the relationship between stress and physical inactivity. He grounded his insights in a recent study that examined the persistent effects of stress on rats. By exposing rats to tail shocks, which acted as a acute stress, and subsequently providing them access to a running wheel, the researchers modeled the choice to exercise. The results of this exercise showed that the stressed rats exhibited a prolonged, significant decrease in voluntary running. This effect was demonstrated for weeks after the shock. Dr. Buhr mentioned that early on in the experiment they realized that they had to figure out how to give the rats more discretion in exercising because if there was a slight propensity to run, the rats were essentially forced to and were capable of running; thus, they had be given an exaggerated choice between running or not, which when given, showed that the rats opted out.
The underlying mechanisms for this behavioral paradigm are rooted in different physiological changes. In the brain, stress weakened the normal dopamine rush in the prefrontal cortex that occurs after (and because of) exercise. The prefrontal cortex is associated with maintaining effortful, motivated behavior, so a decrease in dopamine naturally leads to a decrease in motivated behavior. Simultaneously, rats also showed elevated levels of the protein HSP70 and reduced levels of the antioxidant SOD2, which is indicative of prolonged oxidative stress, a long-term cellular imbalance (between reactive oxygen species and antioxidants) that leads to continuous damage to various classes of macromolecules. HSP70 is a protein that is induced from rising levels of reactive oxygen species and helps neutralize them to help the cell. This leads to the conclusion that stress drains the brain’s motivational neurotransmitters and increases cellular fatigue in the periphery through muscles.
This rodent model contextualizes a 2024 report in human neuroscience from Neuroscience News that details a study from University College London (UCL) titled “Exercise Boosts Motivation to Combat Depression”, which is a sort of inverse to Dr. Buhr’s investiation. The UCL researchers found that aerobic exercises repairs motivation defecitst that were linked to severe stress and depression. It was proposed tey movement systemically decreases inflammation and restores the dopamine function that stress suppresses.
When taking a look at Dr. Buhr’s work and this paper in conjunction, a profound yet slightly cruel biological paradox emerges. Acute stress is a sort of emergency brake on our physical activity; it suppresses our dopamine and drives muscular stress. In contrast, as indicated by the UCL research, exercise is also the primary tool our biological system has to clear that inflammation and reboot our dopamine system, which inclines one to see that our bodies are essentially wired to avoid the exact activity that is necessary to restore our neurochemical balance.
Understanding this dynamic can lead to a change in how we should approach wellness and the concept of burnout. Rather than waiting for motivation to emerge after a stressful event, one should recognize that the physiological reality is that our body is temporarily unable to generate motivation, and realize that one must take a leap and force oneself to reboot the system.
This could lead to a shift in public health campaigns so that instead of telling stressed populations to simply “find motivation”, they could explain that the initial leap of beginning exercise is a treatment for dopamine suppression, which prevents that motivation from being found.
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