Nowadays, exoskeletons have been introduced for empowering walking in military, industrial and rehabilitation settings. Several companies are commercializing these devices, but there is a lack of understanding of their effects on muscle activations and coordination. The objective of this article is to investigate the impact on muscle activation and user effort during ambulatory, robotic-assisted walking. Compared with free walking, our results suggest that robotic assistance with the Exo-H2 lower limb exoskeleton may result in increased muscle activation. Muscular timing experienced unspecific changes with respect to unassisted walking. Further research is needed to unveil the mechanical interaction between the robot and the lower limbs and the underlying motor adaptations in response to robot-assisted walking.