Improvements in workplace productivity at the office offer significant benefits to companies. The time spent in the sitting position has increased currently, and this sedentary position has negative impacts on health. Thus, to promote the health of workers and improve workplace productivity, it is important to encourage physical activity in the office. In this study, we conducted an experiment in the fall of 2016. We divided participants into two groups. In the first group, participants sat at their desks and took breaks while sitting; in the second group, participants walked on a stepper and took breaks while standing. We found that the sympathetic nervous system was activated during work after physical activity. The questionnaire showed that participants who took a break involving physical activity were less likely to complain of fatigue and drowsiness. In addition, the working efficiency for tasks involving idea generation improved after physical activity.