Dopamine is an important brain chemical typically associated with pleasure, motivation, and reward-seeking. Now, a team of scientists led by Johns Hopkins University has found that dopamine also plays a major role in why exercise and other types of physical efforts feel easy to some and exhaustive to others.
The findings could lead to more effective ways to help people establish and stick with exercise regimens, new treatments for fatigue associated with several conditions, such as depression, and a better understanding of Parkinson’s disease, which is marked by a loss of dopamine-producing cells in the brain over time.
“Researchers have long been trying to understand why some people find physical effort easier than others,” said senior author Vikram Chib, an associate professor of Biomedical Engineering at Johns Hopkins. “This study’s results suggest that the amount of dopamine availability in the brain is a key factor.”
While previous research has found that people with higher dopamine levels are more willing to exert physical effort for rewards, the current study focuses on this chemical’s role in people’s self-assessment of effort required for physical tasks, without the promise of rewards. To examine this correlation, the experts enrolled 19 adults diagnosed with Parkinson’s disease with an average age of 67 and asked them to perform three experiments.
In the first experiment, the participants were asked to squeeze a hand grip equipped with a sensor on two different days within two months from each other, and report the level of effort they put forth. While on one of the days they took their standard dopamine medication as they normally would, on the other, they were asked not to take it. When the participants took the dopamine medicine, their self-assessments of units of effort expended were more accurate than when did not take the medicine, meaning they perceived the task to be physically harder without dopamine.
In another experiment, they were given a choice between squeezing with a relatively low amount of effort on the grip sensor, or flipping a coin and taking the chance to have to perform a task with either no effort or a high level of effort. When they took their dopamine medicine, they were more willing to take a chance on having to perform a higher amount of effort than when they didn’t.
Finally, a third experiment offered them the choice between getting a small amount of money or flipping a coin that would either bring them a higher amount of money or no money at all. Since the results showed no difference in their choice whether they took dopamine or not, this chemical’s influence on risk-taking preferences seems to be specific to physical effort-based decision-making.
These findings suggest that dopamine is a critical factor in helping people accurately assess how much effort physical tasks require, which can affect how much effort and motivation they are willing to invest in such tasks. Better understanding the chemistry and biology of motivation may contribute to the development of methods to motivate exercise and physical therapy regimens, as well as help explain the pervasive fatigue present in conditions such as depression or long Covid.
The study is published in the journal NPG Parkinson’s Disease.
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