Abstract: Since Dennis Kimetto ran 2:02:57 in the Berlin Marathon of 2014, the concept of running a sub-2-hour marathon started to gain more and more attention. In the quest for the sub-2-hour marathon, knowledge from lab-based treadmill tests needed to be extrapolated to marathon performance. This allowed for quantification of the effects of course design, innovative footwear and aerodynamic drafting formations on marathon running performance. This presentation will discuss how each of these factors affects running energetics and enabled Eliud Kipchoge’s sub-2-hour in Vienna in October 2019.