A new study in Physiology & Behavior provides evidence that a single bout of exercise can alter how people respond to rewarding situations soon afterward. However, this change appears to depend on whether or not a person has regularly engaged in that exercise before.

“We were interested in the effects of exercise on reward functioning because anecdotally, exercise is one of the best ways to treat a range of psychological disorders, including depression and addiction,” said study author Emily C. LaVoy of the University of Houston.

“A common feature of these psychological disorders is a disruption in the reward functioning centers in the brain. There has been little research examining the effects of acute exercise on reward functioning, with mixed results reported in the literature.”

“Thus, we don’t yet know why exercise seems to exert a beneficial effect in these psychological disorders. In this study, we carefully controlled the intensity of exercise by individually prescribing the exercise bout based on each subjects’ lactate threshold, as there is evidence that an exercise-induced increase in dopamine occurs above lactate threshold.”

“We also chose two measures of reward functioning: an objective measure of motivation for reward, and a subjective measure of pleasurable responses to reward, as a way to assess if exercise was more effective within certain reward processes than others.”

In the study, 35 participants ran on a treadmill for 20 minutes before completing two measures of reward functioning. On another day, the participants sat for 20 minutes before completing the same tests.

The two tests measured the willingness of participants to exert physical effort for monetary rewards and the amount of pleasure associated with receiving a reward.

Overall, the bout of exercise did not increase motivation for and pleasurable responses to rewards.

But the researchers were able to detect opposing effects when they divided the participants into subgroups.

“Those subjects who reported a longer history of running training showed increases in motivation for rewards after exercise, while subjects who reported less history of running training showed decreases in motivation after exercise,” LaVoy told PsyPost.

This did not appear to depend on the overall fitness of the participants. In other words, participants with a history of running did not appear to respond differently just because they were in better shape.

“This suggests that there is a possible conditioned effect of exercise on reward functioning, and interventions should keep in mind people’s preferred mode of exercise,” LaVoy explained.

“We also found that subjects with a higher resting heart rate variability reported lower arousal in response to all emotional pictures after exercise, suggesting that those with high heart rate variability may experience exercise as calming.”

Like all research, the study has limitations. The study examined reward functioning soon after a bout of exercise, but did not examine potential long-term effects.

“It is important to keep in mind that our study examined a healthy adult sample engaging in a single acute bout of exercise,” LaVoy said. “Thus, this may not model the effects of exercise on reward functioning when used as a chronic intervention in healthy or in clinical populations. Future studies ought also to consider whether exercise intensity or the timing of the behavioral measures impacts behavioral outcomes.”

The study, “Effects of an acute bout of physical exercise on reward functioning in healthy adults“, was authored by Margaret C. Wardle, Paula Lopez-Gamundi, and Emily C. LaVoy.