While the effects of aerobic exercise during a cognitive task on the performance of said cognitive task have been extensively studied, it has not been investigated whether cognitive performance during aerobic exercise influences the physical performance. For this, it is the main goal of the study to investigate the physical and cognitive performance during a simultaneous conduction of aerobic exercise and mental rotation. Forty-one German sport students cycled at 60% intensity while simultaneously performing a mental rotation task. In a within-subject design, both physical and cognitive performances were compared with isolated cycling and mental rotation as control conditions using both objective (heart rate and pedal cadence in the cycling task, reaction time and accuracy in the mental rotation task) and subjective (RPE) cognitive and physical measures. The results analyzed with hierarchical linear modeling revealed no effect of either simultaneous cognitive tasks on objective (heart rate) or subjective (RPE) physical effort, nor of simultaneous exercise on reaction time or accuracy in cognitive performance. However, we have found lower cadence during cognitive tasks, which was also stable in time compared to an increase in cadence during exercise control. Furthermore, our results demonstrated increased cognitive effort during exercise. Our findings suggest that increased effort, both physiological and cognitive, is required during combined physical and cognitive work in support of neurological resource conflicts caused by the differing demands of exercise and executive function.