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Physical activity activates brain regions and transmitter systems that represent the reward system (i.e., the ventral striatum [VS] and dopamine). To date, the effect of training status and acute exercise on reward processing has not been investigated systematically in humans. To address this issue, we examined highly trained (HT) physically inactive (PIA) men with a monetary incentive delay (MID) paradigm.We used functional magnetic resonance imaging (fMRI) to investigate the neural correlates of monetary incentive processing after acute exercise. HT and PIA subjects were randomized into two groups. Subjects in one group ran on a treadmill (T) for 30 min at 60%–70% of their maximal oxygen uptake (V˙O2max), whereas subjects in the other group performed placebo exercise (P). Approximately 1 h after exercise, the MID task was conducted. Mood was assessed using the Positive and Negative Affect Schedule before and after the exercise intervention.The psychological assessment showed that exercise significantly increased mood in HT and PIA men. During gain anticipation and gain feedback of the MID task, the VS was significantly stronger activated in the placebo group than in the treadmill group. No effect of training status and no interactions between training status and acute exercise were found.Acute exercise diminishes sensitivity to monetary rewards in humans. This finding is discussed concerning interactions between tonic and phasic dopamine in the VS.