The text below or something similar appears in most or all of the endurance workouts (from 60 minutes out to 4+ hours). I copied this out of Putuo which is a 4:15 endurance workout included in the full triathlon build. I can probably make it through a 90-120 minute endurance ride without any fueling, but doubt that I can longer than that. If I take in carbs (sugar), then doesn’t my body switch to using that for fuel rather than my fat stores?
“Aerobic Endurance workouts are aimed at improving your aerobic (i.e. non-sugar) power producing capabilities in a low-stress manner. By riding for increasingly longer periods of time, your endurance muscle fibers become more efficient at utilizing fat for fuel and sparing sugar stores for more intense efforts.”