Building on self-regulation research and self-determination theory, the present research investigates the causal effects of job demands and job control on physical activity after work. In 2 experiments (total N = 251), participants completed a work simulation that was followed by a physical activity task (cycling on a bicycle ergometer). We simulated a call center, consisting of customer interactions and calculation tasks. In both experiments, job demands (high vs. low) were manipulated between-subjects in terms of customer unfriendliness and task difficulty. In Experiment 2, we also manipulated job control (high vs. low) in terms of decision latitude. As predicted, both experiments showed negative effects of job demands on physical activity, reflecting that time on the bicycle ergometer was lower for individuals in the high demands condition compared to the low demands condition. However, this effect was not mediated by self-regulatory capacities. Regarding job control, we found preliminary evidence for the expected indirect effect on physical activity through increased self-determination. In summary, our results provide causal evidence for the influence of job characteristics on physical activity and, thereby, advance our understanding of the mechanisms underlying the spill-over of work into leisure time. (PsycInfo Database Record (c) 2021 APA, all rights reserved).