When i look at my performance diagnostic for cycling, from a certain point on (~after fat max zone) the amount of fat burned decreases to zero (with increasing wattage) and only carbs are used to produce ATP.
Why is the aerobic system not used anymore?
What i understood / assume so far:
the aerobic system is limited by the vo2max and the absolute usage of this capacity --> from a certain point on the total amount of required ATP can not be produced by the aerobic system
the anaerobic system can produce ATP much faster than the aerobic system
anaerobic and aerobic system can be used in parallel(?) since the aerobic system requires pyruvate.
My best guess:
Both systems share a limiting factor, so from a certain point on the production shifts to the anaerobic system(?)