Exercise is commonly considered one of the best strategies for managing stress; however, is there a chance that the opposite is true? How can the experience of stress affect our desire to exercise? These were among the most interesting questions I had from Dr. Buhr's talk on how stress and trauma may affect people's physical activity. In his presentation, he mentioned a research aimed at exploring how experiencing stress may lead to long-term changes in voluntary physical activity. The experimenters placed rats into a condition of 0, 50, or 100 controllable tail shocks and provided them with access to running wheels. Interestingly, these rats ran approximately two to four times fewer compared to the control group, with this effect remaining stable during the whole nine-weeks period of the study. Moreover, changes were also found in the activity and concentration of dopamine in different brain regions involved in motivation and rewards perception. For instance, it was found that the concentration of this substance was significantly reduced in the striatum, the brain structure responsible for motor actions and motivated behavior. Thus, the mechanism of the negative impact of stress on physical activity might be biological rather than the person's voluntary decision to stop training.
Another recent 2024 publication by Fetcho et al. from Weill Cornell Medicine sheds light on this question as well. In their study, the researchers were interested in the mechanism of how prolonged exposure to stress may affect the animals' decision to perform certain actions. They examined a neural pathway from the anterior cingulate cortex (ACC) to the nucleus accumbens (NAc), brain regions responsible for evaluating rewards and the costs of their obtaining. In the experiment, mice were put into a maze and had a choice of a smaller reward that did not require any efforts and a larger one that required crossing a barrier. Under normal conditions, the mice preferred a larger reward. However, under the disruption of the ACC, they became less willing to perform additional actions for obtaining the bigger reward. Moreover, the researchers exposed mice to corticosterone, a stress hormone, for 21 days. After that, the animals became less interested in pursuing the higher-effort reward and had problems with the activity of the neural pathway from ACC to NAc. However, they were able to distinguish between the size of the rewards in case both of them required the same amount of effort.
The interesting thing about these findings is how similar they are to the research presented by Dr. Buhr. He showed how one stressful experience may lead to long-term decrease in voluntary physical activity, while Fetcho et al. revealed the neural pathway in the brain responsible for the negative effects of the prolonged exposure to stress hormones. Although these studies explore quite different behaviors, they demonstrate that stress may affect motivated behavior in the same way. While the first study demonstrates changes in the neurotransmitters' activity, such as dopamine and serotonin, the second one explores the interactions between two regions of the brain, ACC and NAc. Since NAc belongs to the ventral striatum, an interesting question emerges whether the changes in dopamine signaling and frontostriatal circuits may influence each other and affect exercise motivation. However, the study by Fetcho et al. does not examine physical activity, and neither study proves the connection between them.
However, this connection is extremely interesting because the fact that physical inactivity after the experience of stress may be caused by changes in the brain that lead to the problems with the evaluation of the cost of action is relevant to the exercise problem. Exercise requires some effort from a person even though it is known to be rewarding for his/her health in the future. However, if stress affects the way the brain evaluates the cost of actions, a person might have problems with starting exercises even though he/she realizes their benefits. Therefore, these findings provide valuable information on how stress may change physical activity and why it becomes harder to start training in this situation.
In my opinion, these ideas are especially relevant to my personal experiences as a college student. During busy weeks with many exams, assignments, research work, and other responsibilities, I find it much harder to motivate myself to go to the gym or play basketball although it is usually something that I like to do. Previously, I tended to see this only as a lack of discipline or time management but now Dr. Buhr's presentation made me reconsider this and wonder if stress can also influence the neurological processes in my body. Of course, the stress that I experience is not comparable with the stress that was used in these experiments with animals, but it is interesting to speculate how similar processes take place in humans. In my opinion, these findings are also especially interesting in terms of individuals who are affected by chronic stress and/or trauma. Physical activity is widely used to increase the level of mental well-being, but stress itself may become an obstacle to start training. It creates a vicious circle since physical activity is the very thing that helps someone deal with stress. It would be interesting to conduct further investigations in this area to find out if there are ways to make physical activity more rewarding or less effortful in order to encourage people to start training.
References:
Buhr, Trevor J., et al. “The Persistence of Stress-Induced Physical Inactivity in Rats: An Investigation of Central Monoamine Neurotransmitters and Skeletal Muscle Oxidative Stress.” Frontiers in Behavioral Neuroscience, vol. 17, 2023, article 1169151.
Fetcho, Robert N., et al. “A Stress-Sensitive Frontostriatal Circuit Supporting Effortful Reward-Seeking Behavior.” Neuron, vol. 112, no. 3, 2024, pp. 473–487.e4.
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