Pierre and Nicolette from Mountain Abandon were early adopters of our RPE scale for athlete feedback. In this article they present the science behind RPE, how they track athlete progress/fatigue with this data, and why they believe it develops the athletes inherent ability to self govern. In ultra running and endurance sports, being able to pace yourself correctly and evaluate intensity is key to success in both training and racing. With RPE we have a consistent measurement relaying only on the athletes brain, overcoming issue with poor data from devices which cannot know weather temperatures, caffeine consumption, sleep deprivation and other variables.