New research from engineers at the University of Colorado Boulder (CU Boulder) sheds light on why people move faster when they are happy. The study shows how the brain chemical, Dopamine, influences movement speed in response to rewards, offering insights that could help researchers better understand conditions such as Parkinson’s disease and depression, where movement and motivation are often impaired.
The findings were published on 27 February 2026 in the journal Science Advances.
“Anecdotally, we just feel that this is true,” said senior author Alaa Ahmed, professor in the Paul M. Rady Department of Mechanical Engineering at CU Boulder. “When you go to the airport to pick up your parents, you may run to greet them. But if you’re picking up a colleague, you’re probably just going to walk.”
Ahmed and Colin Korbisch, a former graduate student at CU Boulder, designed an experiment to examine how reward signals affect human movement. Participants used a joystick-like device to reach for targets displayed on a computer screen. Successful reaches triggered rewards in the form of a flash of light and a beeping sound.
One of four targets always delivered a reward, one never did, and two provided rewards unpredictably.
Participants consistently moved faster towards targets with a higher likelihood of reward. When they aimed for a low-probability target and unexpectedly received a reward, their movement vigour increased sharply, even after the reward had been delivered. This change occurred just 220 milliseconds after the beep, too subtle to detect with the naked eye but clear in data analysis.
“Movements are a window to the mind,” Korbisch said. “Normally, you can’t go into the brain and see what the dopaminergic neurons are doing, but movement could reflect those neural computations that are so difficult to disentangle.”
The researchers propose that this post-reward burst reflects a second pulse of dopamine triggered by the pleasant surprise. When rewards were certain and expected, no additional increase in vigour appeared after delivery.
“Importantly, this effect wasn’t tied to reward reception alone,” Korbisch said. “If the outcome was certain and known to the individual, we saw no further increase in vigor.”
Scientists have long recognised dopamine’s role in learning. In the 1990s, neuroscientist Wolfram Schultz conducted experiments on primates, showing that dopaminergic neurons fire in response to expected rewards, such as a drop of apple juice after a bell rings. Dopamine activity increases even before the reward arrives. If the expected reward does not materialise, activity dips below baseline, creating what researchers call a “reward prediction error.” This process helps the brain learn which actions are worthwhile.
The CU Boulder results mirror these established dopamine response patterns, suggesting that the same reward prediction signals also shape how vigourously people move.
Recent reward history influenced behaviour as well. Participants who experienced streaks of success tended to move faster overall, while repeated disappointments slowed them down.
Ahmed noted that movement patterns change in several medical conditions. People with Parkinson’s disease, who lose dopaminergic neurons, often struggle to initiate and speed up movements. Depression is also associated with slowed actions. Ahmed suggested that tracking movement vigour over time could eventually provide a non-invasive way to monitor health.
“If you’ve had a good day, you’ll go faster. If you’ve had a bad day, you’ll move slower,” Ahmed said. “It’s basically that skip in your step.”
The study builds on earlier research linking dopamine to effort-based decisions and motor control, offering a behavioural measure of internal motivational signals that are otherwise difficult to observe directly.