Research is scarce on ways to enhance the effect of rest breaks during mentally demanding tasks. The present study investigated the effectiveness of two restbreak interventions on wellbeing during an academic lecture. Sixtysix students (53 females, mean age 22.5 years) enrolled in two different university classes of 4hr duration participated in the study. Two measures of wellbeing (fatigue and vigor) were assessed immediately before, after, and 20 minutes after the break. A control condition without a break as well as an unstructured break was compared with breaks either encompassing physical activity or a relaxation exercise. Compared with the nonbreak condition, the unstructured rest break led to an increase in vigor, the exercise break as well as the relaxation break both to an increase in vigor and a decrease in fatigue at 20min post break. Compared with the unstructured break, exercise led to an (additional) increase in vigor and relaxation to an (additional) decrease in fatigue at 20min post break. Thus, the effects of rest breaks during mentally demanding tasks can be enhanced by engaging in physical activity or relaxation exercises, with effects lasting at least as long as 20 min into the continuation of the task.