The Guided workouts in the Virtual Active Run and Hike series use RPE as a way to recommend and monitor your effort.
RPE stands for “rate of perceived exertion.” It is a one to ten measurement of how hard you are exercising, with one being an easily sustainable effort and ten being the edge of your physical limitation.
RPE is often related to your maximum heart rate (MHR). Learn more in the related support article.
Other guided BitGym content such as Cardio Coach uses Color Zones, which are also similarly based on self-evaluated exertion level.