Dopamine The secret ingredient for effortless exercise?

A study by researchers at Johns Hopkins Medicine suggests that dopamine, a brain chemical associated with pleasure and motivation, plays a vital role in how people perceive the amount of physical effort required for a task, especially in people with Parkinson\’s disease, a condition characterized by a lack of dopamine.

A new study led by Johns Hopkins Medicine researchers indicates that dopamine, a neurotransmitter traditionally linked to pleasure, motivation and reward-seeking, also appears to be a key factor in determining why physical activities seem easy for some individuals while they prove to be draining for others. This conclusion was drawn from the study of people with Parkinson\’s disease, a condition characterized by the progressive loss of dopamine-producing cells in the brain.

The study, recently published in npj Parkinson\’s diseasecould potentially pave the way for the development of improved methods of encouraging people to adopt and maintain exercise routines. It could also lead to new treatments for fatigue related to depression and a range of other conditions, as well as improve our understanding of Parkinson\’s disease, according to the researchers.

Researchers have long sought to understand why some people find physical exertion easier than others, says study leader Vikram Chib, Ph.D., an associate professor in the Department of Biomedical Engineering at Johns Hopkins University School of Medicine and researcher at the Kennedy Krieger Institute. The results of this study suggest that the amount of dopamine available in the brain is a key factor.

Chib explains that after a bout of physical activity, people\’s perceptions and self-ratings of the effort they\’ve expended vary, and it also guides their decisions about undertaking future efforts. Previous studies have shown that people with increased dopamine are more willing to exert physical effort for rewards, but the current study focuses on the role of dopamine in self-assessment of the effort required for a physical activity, without the promise of a reward .

For the study, Chib and his colleagues at Johns Hopkins Medicine and the Kennedy Krieger Institute recruited 19 adults diagnosed with Parkinson\’s disease, a condition in which dopamine-producing neurons in the brain gradually die out, causing involuntary, uncontrollable movements such as tremors. , fatigue, stiffness, and problems with balance or coordination.

In the Chibs lab, 10 male and nine female volunteers with a mean age of 67 were asked to perform the same physical task by squeezing a sensor-equipped handle on two different days within four weeks of each other. . On one of the days, the patients were asked to take their standard daily synthetic dopamine medication as they normally would. On the other hand, they were asked not to take their medications for at least 12 hours before performing the compression test.

On both days, patients were initially taught to squeeze a grip sensor at various defined effort levels, then were asked to squeeze and report how many units of effort they put in.

When the participants were on their regular synthetic dopamine medication, their self-reports of units of effort expended were more accurate than when they were off the medication. They also had less variability in their efforts, showing precise squeezes when the researchers asked them to squeeze at different effort levels.

Conversely, when patients had not taken the drug, they consistently overestimated their efforts, meaning they perceived the task to be more physically difficult and had significantly more variability between intakes after being challenged.

In another experiment, patients were given the choice between the safe option of squeezing with relatively low effort on the grip sensor or tossing a coin and taking the risk of no effort or a very low level of effort. high. When these volunteers were on their meds, they were more willing to take the risk of having to perform more effort than when they were off their meds.

A third experiment gave participants the choice between getting a small guaranteed amount of money or, with a toss of a coin, getting nothing or a larger amount of money. The results showed no difference in the days the subjects took the drugs and when they didn\’t. This result, say the researchers, suggests that the influence of dopamine on risk-taking preferences is specific to decision-making based on physical exertion.

Together, Chib says, these findings suggest that dopamine level is a critical factor in helping people accurately gauge how much effort a physical activity requires, which can significantly influence how much effort they\’re willing to put in. for future activities. For example, if someone perceives that a physical task will require extraordinary effort, they may be less motivated to do it.

Understanding more about the chemistry and biology of motivation could advance ways to motivate exercise and physical therapy regimens, Chib says. Furthermore, inefficient dopamine signaling could help explain the pervasive fatigue present under conditions such as depression and long-term COVID, and during cancer treatments. Currently, he and his colleagues are studying the role of dopamine in clinical fatigue.

Reference: Dopamine Facilitates Translation of Physical Effort into Effort Ratings By Purnima Padmanabhan, Agostina Casamento-Moran, Aram Kim, Anthony J. Gonzalez, Alexander Pantelyat, Ryan T. Roemmich, & Vikram S. Chib, April 1, 2023, npj Parkinson\’s disease.
DOI: 10.1038/s41531-023-00490-4

Other researchers who participated in this study include Purnima Padmanabhan, Agostina Casamento-Moran and Alexander Pantelyat of Johns Hopkins; Ryan Roemmich of the Johns Hopkins and Kennedy Krieger Institutes; and Anthony Gonzalez of the Kennedy Krieger Institute.

The study was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institute of Healththe National Institutes of Mental Health and the National Institute of Aging.