Why do some people find it difficult to do the same exercise while others do it with ease? New research suggests that dopamine, a neurotransmitter linked to pleasure, motivation and reward-seeking, appears to play a key role in this process. Dopamine plays an important role in how people perceive the amount of physical effort required for an activity. This is the result of a study on patients with Parkinson’s disease, which is characterized by a gradual loss of dopamine-producing cells.
The study, led by Johns Hopkins University researchers, could help find improved ways to encourage people to adopt and maintain exercise routines. According to the research team, this could lead to new treatments for fatigue associated with depression and various other conditions, as well as advance our understanding of Parkinson’s disease.
“Researchers have long tried to understand why some people feel physical exertion more easily than others,” said Vikram Chiev, a professor at the University’s School of Biomedical Engineering. “Our results show that the amount of dopamine available in the brain is important. It implies that it is an element,” he said.
He explains that people’s perceptions and self-reports of effort expended after performing a physical activity vary, which influences their ability to continue the same effort in the future. For example, if someone perceives that physical work requires a tremendous amount of effort, their motivation to exercise may decrease.
Previous studies have shown that people with increased dopamine are more willing to exert physical effort for a reward. The study focuses on the role of dopamine in people’s self-assessment of effort required for physical tasks without the promise of reward.
Nineteen patients with Parkinson’s disease volunteered for the study. With an average age of 67 years, 10 men and 9 women were asked to perform the same physical task for 2 days using a sensor-equipped device within 4 weeks. On one of these days, the general synthetic dopamine drug was taken as usual. On other days, they were asked to take no medication for at least 12 hours prior to testing. On both days, patients self-reported how much effort they exerted after squeezing the grip sensor.
Self-ratings of effort expended in activities were more accurate when taking dopamine pills than when taking no pills. Participants also consistently overestimated their efforts when not taking the drug. In other words, it was perceived as physically more difficult work.
In another experiment, patients were asked to choose between an activity requiring relatively low effort and an option that allowed them to perform a very high level of effort. Patients were willing to take the opportunity to perform more effort when taking the drug than when not taking the drug.
These findings suggest that dopamine levels are an important factor in helping people make accurate assessments of how much effort physical tasks require, and that this can significantly influence how much effort they will expend for future tasks.
“Understanding more about the chemistry and biology of motivation can advance ways to motivate exercise and physical therapy therapies,” said Professor Chiev. “It may help explain the fatigue that occurs during exercise.”
The study was published in ‘npj Parkinson’s disease’. The original title is ‘Dopamine facilitates the translation of physical exertion into assessments of effort.